The Long Term Development Statement and Shared Network Data

Illustrative LTDS network explorer

The explorer shows how the LTDS products fit together on a worked, synthetic network. It includes a CIM Profile lens that groups equipment by the profile that carries it, so the structure of the grid model is visible alongside the network view.

The same network seen as physical geography, with the voltage cascade, the network owners and capacity screening by postcode, is on the network map.

The LTDS reform story, from network disclosure to data infrastructure

Although the core duty remains that distribution licensees publish planning information for the networks they operate, the delivery model is changing. The older LTDS was mostly a human-readable statement, useful for transparency but hard to compare across licence areas and hard for software to reuse. Heat pumps, electric vehicles, storage, distributed generation, flexibility and local energy planning all depend on a clearer view of distribution-network capability. The reformed LTDS adds two machine-readable products: a Common Information Model grid model and a Capacity Heatmap in a common structure.

Rather than treating regulation and schema design as one activity, the architecture separates regulatory intent from technical implementation. The regulatory layer says what must be published and when, while the technical layer defines the model, profiles, constraints and validation route. Ofgem owns the Direction, the Form of Statement and derogation decisions. The BSI GB CIM Engagement Hub is the public technical location for current artefacts and version history. That split matters because a schema correction is not the same thing as a change in regulatory intent.

The learning sequence starts with the network view before moving into legal and data-model detail, then explains the purpose, legal chain, publication family, model contents, CIM profiles, validation route and wider governance boundary.

The LTDS as the distribution planning disclosure

The Long Term Development Statement, usually shortened to LTDS, is the regulated statement through which each electricity distribution licensee describes the characteristics and expected development of its network. The obligation is long-standing and is mandated through a direction made under paragraph 25.2 of the standard conditions of the Electricity Distribution Licence.²

The practical purpose is to give a connection applicant, local authority, flexibility provider, modeller or policy team a first view of network capability before committing time and money to detailed studies. The Form of Statement says the LTDS should give a high-level understanding of the network, provide information for initial assessments of network capability, describe development proposals and identify the correct points of contact.³

The LTDS should be read as a planning disclosure rather than a live control-room model, a connection offer, a reservation of capacity or a substitute for the detailed engineering studies carried out during a connection application. Its job is to turn hidden network knowledge into an auditable starting point for better questions.

Why the energy transition made the LTDS more important

Distribution networks were built mainly to move electricity from the transmission system down to homes and businesses. They now host growing volumes of distributed generation, storage, electric-vehicle charging, heat pumps and flexible demand. The same network must be planned for demand, export, congestion, flexibility and local spatial growth.

Shared information is now central to good planning because each participant needs a reliable first view of the same network capability. A developer needs to know where a connection may be feasible, a local authority needs credible network inputs for local energy planning, and a flexibility provider needs to identify places where capacity constraints may create value. NESO and transmission companies need better visibility of distribution-network behaviour for whole-system planning. Software developers need stable, machine-readable structures before they can build reusable tools.

The LTDS addresses this information problem by creating a common regulatory structure for public distribution-planning information. The 2024 reform added grid models based on the Common Information Model and standardised Capacity Heatmap data, with the stated aim of improving consistency, accessibility and usability.¹

The legal chain from the Electricity Act to the Form of LTDS

Standard Licence Condition 25.2 gives Ofgem the power to specify the form in which the LTDS is published. The Direction issued on 30 April 2024 uses that power. It directs each licensee to publish an LTDS consistent with the Form of Statement and sets expectations for publication dates and Grid Modelling Data Result deadlines.²

The Form of Statement is where most practical detail sits. It defines the sections of the LTDS, the data to be included, the required file formats, update cycles, data-security provisions and the phased implementation plan. The Direction creates the obligation; the Form of Statement defines the deliverable.³

At each step in the legal chain, broad statutory authority narrows into a specific LTDS deliverable. The Electricity Act 1989 creates the licensing regime, the Distribution Licence carries standard conditions, SLC 25.2 confers the power to direct, the Direction applies that power to LTDS publication, and the Form of Statement defines the content that must be produced.

The notification process in the Direction requires a licensee that becomes aware it cannot meet a relevant publication date or Grid Modelling Data Result deadline to notify the Authority in writing as soon as reasonably practicable, and in any case no later than 28 days before the relevant date, and explain why. The Direction then provides for a revised date or deadline to be set, taking reasonable account of the circumstances. The clause was introduced in response to consultation feedback recorded in the accompanying Direction Letter,⁴ and it is the mechanism through which each later derogation was made.²

Ofgem and the BSI-hosted GB CIM Engagement Hub operate as parallel authority routes: Ofgem maintains the Direction, the Form of Statement and the derogation decisions, while the current technical artefacts, schemas and version history are maintained through the Hub. The current regulatory position sits with Ofgem; the current technical artefacts sit with the Engagement Hub.¹⁹

The licensees that publish LTDS data

The obligation sits with the holders of electricity distribution licences. Great Britain has fourteen distribution licence areas operated within six main DNO groups. Each licensed area is responsible for its own LTDS publication, even where several licence areas share a corporate group.

The distinction between a DNO group and a licensee matters because the LTDS requirement attaches to the legal entity holding the licence for a defined area, not to the corporate group as a whole. Users will often reach the files through a group data portal, but the model and its metadata should identify the relevant licence area.

The table reconciles to fourteen licence areas across the six groups: ENWL 1 + NGED 4 + NPG 2 + SPEN 2 + SSEN 2 + UKPN 3 = 14. Each area holds one Electricity Distribution Licence and publishes one LTDS, so "14 licence areas", "14 licensees" and "14 LTDS publications per cycle" describe the same count from three angles. The current legal entity names should be taken from the Ofgem public register and the relevant LTDS publication.⁵

The fourteen licensees, named in the Energy Networks Association letter that accompanied the November 2024 derogation request, are: Electricity North West Limited; Northern Powergrid (Northeast) plc; Northern Powergrid (Yorkshire) plc; SP Distribution plc; SP Manweb plc; Scottish Hydro Electric Power Distribution plc; Southern Electric Power Distribution plc; Eastern Power Networks plc; London Power Networks plc; South Eastern Power Networks plc; National Grid Electricity Distribution (East Midlands) plc; National Grid Electricity Distribution (West Midlands) plc; National Grid Electricity Distribution (South West) plc; and National Grid Electricity Distribution (South Wales) plc.⁵

The LTDS publication family: narrative, model and heatmap

The LTDS is a family of products, not a single file. The Form of Statement divides it into an introductory section, summary information, detailed information, development proposals, grid modelling and Capacity Heatmaps.³

The introductory, summary, detailed and development sections provide explanatory and tabular information. The grid modelling section provides CIM data. The Capacity Heatmap provides a standardised data product, with a heatmap narrative to help users interpret it. The three product types answer different questions: what the network is, how it is represented for analysis and where capacity may be screened quickly.³

The annual and bi-annual LTDS publication cadence

The LTDS does not move on one publication rhythm. Section 7.2 of the Form of Statement sets several rhythms, because narrative, development-project updates, grid models and heatmap data age at different speeds.³

• The introductory and summary information is refreshed annually and published on or before 30 November.
• The detailed information is refreshed annually and published on or before 30 November.
• Development proposals are updated annually in November. A May supplement provides updates to firm development proposals and generation data on or before 31 May.
• Grid Modelling and Capacity Heatmaps are each refreshed and published twice a year, on or before 31 May and 30 November.

The introductory section is made available without requiring registration. Other sections are made available on the licensee website following registration of user details. The statement is free of charge unless Ofgem decides otherwise.³

Transitional implementation dates can sit close to, but not exactly on, the steady-state dates. The current Stage 2 publication date, for example, is 29 May 2026 rather than 31 May. The Ofgem LTDS decision page remains the source for the live regulatory timetable.¹

The grid model as a structured view of the network

The grid model is a machine-readable description of the distribution network within the LTDS modelling scope. It represents physical equipment, how that equipment is connected, selected electrical characteristics, system-capacity information, short-circuit information, locations, operating assumptions and calculated results where required.

The 2024 Form of Statement requires descriptions of both the existing network and the expected future network. For the existing network it envisages solved cases and models that describe capacity, characteristics, non-coincident loadings, fault levels and recent connection activity. For future years it requires models of the anticipated physical network and bus loadings, together with Difference Models for firm development projects.³

The exact current classes, attributes, profiles and constraints are technical artefacts. They change through controlled governance, so the BSI GB CIM Engagement Hub is the place to check the active version before implementation.⁹

CIM as the common language for network models

The Common Information Model (CIM) is a family of standards for describing power-system information in a consistent way. It gives equipment and relationships shared meanings. A transformer, switch or line is represented as a typed object with defined properties, rather than as an unstructured row whose meaning depends on a local spreadsheet. The decision to adopt CIM as the GB data standard was set out in an Ofgem open letter in January 2022.⁸

Profiles make CIM usable by selecting the classes, attributes and relationships needed for a particular exchange, because the full model is too broad for one publication product. The LTDS uses profiles derived from CGMES, with GB-specific extensions or deviations where distribution-planning requirements justify them. The profile family can be understood as seven CGMES-derived profiles plus three GB-specific profiles for system capacity, short-circuit results and header metadata, 7 + 3 = 10. The active set and version are maintained on the BSI GB CIM Engagement Hub.⁹

The practical picture is that equipment does not wire straight into other equipment, in the same way that two roads do not merge without a junction. A ConnectivityNode is that junction. A Terminal is the slip road that takes one piece of equipment onto it. In precise terms, equipment connects through Terminals to ConnectivityNodes, and two pieces of equipment are connected when both have a Terminal that references the same ConnectivityNode.

A model is interoperable only when more than the file format matches. The sender and receiver need the same meaning for each field, the same profile version, persistent identifiers, compatible validation rules and a shared process for resolving issues. This is why the technical artefacts and their governance matter as much as the file format.⁹

<cim:Substation rdf:ID="_a3e7d2f1-6c41-4d83-9b27-e0815c9a1b48">
  <cim:IdentifiedObject.mRID>a3e7d2f1-6c41-4d83-9b27-e0815c9a1b48</cim:IdentifiedObject.mRID>
  <cim:IdentifiedObject.name>OSPREY Primary</cim:IdentifiedObject.name>
  <cim:Substation.Region rdf:resource="#_subregion-east-midlands"/>
  <cim:PowerSystemResource.PSRType rdf:resource="#_psrtype-primary"/>
</cim:Substation>

<cim:VoltageLevel rdf:ID="_vl-osprey-33kv">
  <cim:IdentifiedObject.mRID>vl-osprey-33kv</cim:IdentifiedObject.mRID>
  <cim:VoltageLevel.Substation rdf:resource="#_a3e7d2f1-6c41-4d83-9b27-e0815c9a1b48"/>
</cim:VoltageLevel>

Illustrative LTDS SHACL validator

The validator turns the CIM explanation into a testable workflow. It loads an illustrative sample, or takes a pasted or uploaded CIM file, and runs it against the LTDS Equipment-profile SHACL shapes bundled with the validator. The current authoritative artefacts are maintained on the BSI GB CIM Engagement Hub, so a published file should always be checked against the active version there. The report groups findings by severity and can be downloaded.⁹

Full Models, Difference Models and solved cases

A Full Model is a snapshot of a defined part of the system that conforms to one or more profiles. A Difference Model describes changes that can be applied to a Full Model. The Form of Statement uses Difference Models particularly for firm grid-development projects.³

Future-network publication stays manageable when a licensee can publish a base model and a controlled description of additions, removals or changes, rather than describing an entire future network independently for every project. Persistent identifiers allow software to apply the difference to the correct objects.

A solved case combines equipment and topology with an operating scenario and the calculated results of network analysis, going beyond structural description. The result may include power flows and voltages for the scenario. Solved cases are planning studies, not live operational telemetry.

Capacity Heatmaps as the accessible screening product

Capacity Heatmaps are separate from, but complementary to, the CIM grid models. The Form of Statement says their purpose is to let users assess generation and demand capacity, display capacity geographically and perform analytics on pre-computed values without requiring power-flow, state-estimation or short-circuit software.³

This makes the heatmap the more accessible starting point for many users. A planner can screen substations or circuits and identify where further investigation may be worthwhile. The grid model is the deeper analytical product, for users who need network topology, equipment relationships and electrical studies.

A heatmap value is not a promise that a connection will be offered. Capacity changes as new connections are accepted, reinforcement is delivered, network configurations change, and detailed studies reveal constraints that a high-level screening product cannot capture.

The LTDS stage schedule after the published derogations

The 2024 reform was introduced in stages so that DNOs, users and software vendors could develop and test capability before complete models were required. The original dates were later revised through published Ofgem decisions.¹

The current public Ofgem page records Stage 1.3 publication on 28 November 2025, Stage 2 publication on 29 May 2026, Stage 3 publication on 30 November 2026 and Capacity Heatmap publication on 29 May 2026.¹

The May 2026 decision is best understood as architectural control, not only schedule movement. It approved one future-year Equipment and System Capacity model at Stage 2, with the remaining future-year models deferred to Stage 3. It approved a dedicated Short Circuit Result profile, moved connections activity into the Capacity Heatmap, and moved the Stage 3 production deadline from 15 August 2026 to 15 October 2026. The Stage 3 publication date remained 30 November 2026.⁷

Derogations as controlled implementation decisions

In this context, a derogation letter is a published regulatory decision dealing with a specific implementation problem. It should not be read as a general release from the LTDS obligation. Each letter exercises the SLC 25.2 power to vary the publication dates the Direction sets, and in the May 2026 case the Stage 2 contents, after the licensee has notified the Authority under the Direction's own notification clause.²

The May 2026 decision is a useful example of controlled implementation. The question was not whether an output could be produced, but whether the output would be reliable, interpretable and useful. The decision preserved accountability by limiting the approval, keeping both publication dates and requiring at least two rounds of stakeholder engagement after Stage 2 publication to test the approved changes and inform Stage 3.⁷

The obligation on dates is a best-endeavours obligation, while the deliverable the Form of Statement defines is absolute. The notification clause is the procedural valve that turns an anticipated best-endeavours shortfall into a formally varied deadline before the date passes rather than after it. The Electricity Act, SLC 25.2 and the Form of Statement are untouched by a derogation; only the Direction's deadlines, and in May 2026 the Stage 2 contents, are varied.²⁷

The Ofgem and BSI boundary for LTDS governance

The governance model deliberately separates regulatory and technical responsibilities so policy intent and schema maintenance do not blur. Ofgem retains the Direction, the Form of Statement and derogation decisions, while the current technical artefacts, current versions and version history are available through the BSI-hosted GB CIM Engagement Hub.¹⁹

The BSI GB CIM Engagement Hub supports collaboration by providing access to LTDS documentation, decisions on GB CIM and relevant standards updates. It is also the primary public route for technical, policy or business queries about existing schema and for requests for new profiles.⁹

The technical artefacts moved from the Energy Networks Association to the BSI Engagement Hub during 2025, and the 13 May 2026 derogation letter confirmed the Hub as the location of record for the data-exchange definition artefacts, while the Form of Statement, the Direction and the derogation letters remain with Ofgem.⁷

This arrangement lets technical detail evolve without treating every schema correction as a new policy decision. The boundary is the core governance control: technical governance maintains profiles and artefacts, while Ofgem retains responsibility for the regulatory requirement.

Data quality, security and limits on interpretation

A model can conform to a schema and still be wrong. Conformance checks whether the file follows the required structure and constraints. It does not prove that every asset, rating, forecast or scenario is accurate. Reliable use therefore requires both technical validation and engineering assurance.

The Form of Statement requires LTDS data to be subjected to Open Data Triage and to comply with relevant legal, security, privacy and resilience requirements.³ This may affect the level of detail that can be made public. Security should not be used as a vague reason for poor data, but openness should not override the legitimate protection of sensitive information.

• Check the publication date and profile version before comparing files.
• Read the model assumptions and narratives before interpreting capacity or forecasts.
• Distinguish a pre-computed capacity value from the outcome of a detailed connection study.
• Do not treat forecast years as commitments. They reflect the information and assumptions used when the model was prepared.
• Raise schema and governance issues through the BSI Hub. Raise licence or regulatory issues through the relevant Ofgem route.

The LTDS relationship with GC0139 and the Data Sharing Infrastructure

GC0139 sits outside the LTDS because it is a Grid Code modification for planning-data exchange between NESO and Network Operators, not a public LTDS publication duty. As of 7 April 2026 it was pending an Authority decision. The proposal would increase the scope and detail of planning-data exchange between NESO and Network Operators. Network Operators would submit solved sub-transmission power-system models and supporting schedules in weeks 2 and 28; NESO would provide transmission-system models in weeks 12 and 38. The exchange would largely use CIM based on CGMES version 3 with a separate Grid Code profile.¹⁰¹¹

GC0139 is not a public publication and it does not replace the LTDS. It is a regulated exchange between organisations for coordinated planning. The LTDS can still help, because it develops distribution modelling capability, common terminology, software support and GB CIM governance. The GC0139 Final Modification Report recognises the interaction and the possibility that some implementation work is already being undertaken through LTDS modernisation.¹¹

The Data Sharing Infrastructure addresses governance, process and technology for secure data and model sharing at scale, which is wider than the LTDS publication requirement. The LTDS defines specific distribution-planning data products; the Data Sharing Infrastructure may provide a wider trust and sharing layer. One should not be used as a shorthand for the other.

Ofgem's work on architectural coordination makes the strategic point: energy digitalisation needs a coherent direction and structured coordination to minimise cost and avoid duplication. The LTDS is a bounded example of that approach, not proof that all wider coordination problems have been solved.¹²

Practical LTDS workflows by user group

Each practical workflow starts with the least specialist product that can answer the first decision, then moves toward the model or the formal process when more precision is needed.

What a competent LTDS user should retain

1. The LTDS is a regulated statement, not merely an open-data portal.
2. Different sections follow different publication cycles. Grid models and heatmaps are bi-annual; much of the narrative is annual.
3. The LTDS provides planning information for initial assessment. It is not a live network model or a connection decision.
4. CIM improves interoperability only when semantics, profile versions, identifiers, validation and governance all align.
5. Capacity Heatmaps and grid models are complementary products for different levels of analysis.
6. Ofgem controls the regulatory requirement. The BSI Engagement Hub maintains the current technical route.
7. Derogation decisions are targeted implementation controls. Read each one for its exact scope.
8. GC0139, if approved, is a separate bilateral Grid Code exchange. LTDS experience can support it, but does not implement it.
9. Record the publication, date, licence area and technical version used for any LTDS analysis.

Primary sources for the LTDS

The source register points to primary sources rather than separate file copies. The regulatory instruments are on the Ofgem decision page, and the current technical artefacts are maintained on the BSI GB CIM Engagement Hub, where some material requires registration. The citations link to stable canonical pages.

Energy-system topics governed outside the LTDS

Several adjacent topics sit outside the LTDS boundary and need separate treatment.