The Great Britain energy sector dictionary in May 2026, and the regulatory instruments every term resolves to

Where the dictionary stands in May 2026

The dictionary holds two hundred and twenty regulated terms in May 2026. The number rose by sixteen in the twelve months since May 2025, driven by three regulatory currents that introduced new vocabulary into the GB sector. The Data (Use and Access) Act 2025 received Royal Assent on 19 June 2025 and its first commencement orders landed in February 2026, bringing Section 138 (smart-data schemes) and the bulk of Part 5 (data protection) into force.^{3 4 5} The Act introduced fourteen new terms into the data layer, now entered into the dictionary alongside their predecessors under the 2018 Data Protection Act, with cross-references between the pairs where the new term retains or replaces the older meaning. The third LTDS derogation letter of 13 May 2026 reshaped the Stage 2 deliverables and moved short-circuit results from the System Capacity profile (SYSCAP) into a dedicated Short Circuit Results profile (SCR), introducing two more profile-level terms into the data-layer cluster.⁶ The Heat Networks (Market Framework) Amendment Regulations brought Ofgem in as the heat-networks regulator on 27 January 2026, which adds the heat-networks vocabulary to a dictionary that had been electricity-and-gas focused.

The dictionary sits in the workspace between the inline tooltip glossary (which gives a one-line definition wherever an acronym appears in running prose) and the regulatory instruments themselves (which carry the binding text). The tooltip is for the reader who wants to keep reading without breaking stride. The dictionary is for the reader who needs the longer definition, the cross-references to related terms, and the citation pointer to the source where the term was first defined and where it is currently maintained. Both exist because the two reading modes are different: the tooltip is a short verification, the dictionary is the place to settle a disputed reading by checking the instrument the term resolves to. A confusion between two terms (say between the Distribution Code DPC4 voltage-management procedure and the Grid Code OC1 voltage-management procedure) is settled by reading the instrument paragraph, not by reading another paraphrase. The dictionary takes the reader to the instrument by the shortest route.

The other change in 2026 is the way authority is treated for each entry. SLC 25.2 of the Electricity Distribution Licence is the parent instrument that produces the Long Term Development Statement; the Licence is the child of Section 6(1)(c) of the Electricity Act 1989; the Act is the parent of the licensing regime that holds every distribution-code voltage limit and every Engineering Recommendation.^{1 2} A dictionary entry has to point at the right layer in that chain. For an entry on the LTDS the right citation is SLC 25.2 (the instrument that produces the publication) plus the most recent direction or derogation letter (the instrument that shaped the current cycle). For an entry on the Distribution Code the right citation is the Code itself plus the Distribution Code Review Panel's most recent issue. For an entry on a piece of Engineering Recommendation vocabulary (G98, G99, G5/5, P29) the right citation is the Engineering Recommendation, not the parent Code. The dictionary makes that distinction visible on every entry so a reader checking the source can land on the right page in a single step.

What this dictionary is and how it differs from a flat glossary

A glossary lists terms in alphabetical order and gives each one a definition. A dictionary in the working sense used here does three things a glossary does not: it cites the instrument the term resolves to, it carries the date the entry was last verified, and it cross-references the terms that are related to the current entry. The third of those is the one that does the most work in practice. A search for "LTDS" lands the reader on the LTDS entry, but the entry itself carries pointers to SLC 25.2 (the parent instrument), to the Common Information Model (the data standard the LTDS now uses), to SHACL (the shape language that constrains the LTDS profiles), to the Distribution Code (the sibling instrument that governs the operational rules the LTDS planning data feeds), and to the Distribution Network Operator entries (the licensees that publish the LTDS). The reader who arrives looking for one term leaves with a map of the cluster the term sits in.

The other distinction is provenance. Each entry records the document title, the publication date, the locator paragraph, and, where available, the exact wording quoted from the source. Each definition is written against that exact wording rather than against a paraphrase of the instrument, and the date it was last checked is recorded. This is the same discipline the rest of the notes run on, and it is why a dictionary entry can be trusted to be current rather than a snapshot from when it was first written.

The third distinction is reading level. The first paragraph of every entry is plain English: the kind of definition suited to a lawyer or a policy lead with no power-engineering background who has run across the term in an Ofgem consultation paper and wants to know what it means before reading another page of the consultation. The second paragraph is the technical note: the kind of definition written for a network planner, a settlement engineer, or a CIM modeller who already knows the territory and wants the precise reading. The two-paragraph shape is deliberate. A reader can stop after the first paragraph and have a usable definition; a reader who needs the technical reading carries on. The Data (Use and Access) Act 2025 entries are where the two-paragraph shape pays the largest dividend, because the Act introduced terms (smart data, data holder, data user, gatekeeper) that have a plain-English reading in one register and a strict statutory reading in another.³

The fourth distinction is what the dictionary deliberately does not do. It does not editorialise. An entry for a market design feature (zonal wholesale pricing, reformed national pricing) records what the feature is and where it is defined; it does not record a view on whether the feature is the right design. The opinions live elsewhere on the workspace, set out with the reasoning that supports them. The dictionary is the part of the workspace that has to remain neutral so that two readers with different views on a topic can both check that they are using the same vocabulary before they disagree.

The dictionary search, with full-text matching across term, abbreviation, and related-term fields

The search below indexes the two hundred and twenty entries as the reader types. The match is fuzzy: typing "ltds" or "long term development" both land on the LTDS entry; typing "slc 25" lands on the parent licence condition. The fields searched in order of weight are the abbreviation (highest), the canonical term, the related-terms array, the plain-English definition, and the technical note. A search returns the top ten matches with the match field highlighted, and the reader can open any match to read the full two-paragraph entry with citation tag and as-of date.

The filters narrow the index in four ways. The domain filter (network, markets, data, governance, gas, voltage, statute) narrows by the cluster a term sits in. The authority filter (Ofgem, NESO, DESNZ, Elexon, ENA, BSI, the National Audit Office) narrows by the body that publishes or maintains the parent instrument. The verified-since filter narrows by the as-of date so a reader checking the consistency of a recent consultation against the current vocabulary can isolate the entries verified inside the last quarter. The instrument filter (Act, licence condition, code, Engineering Recommendation, technical standard) narrows by the kind of source the term resolves to. The four filters combine, so a reader looking for all data-layer terms maintained by Ofgem and verified inside the last quarter can find them in two clicks.

Statutory terms: the Electricity Act 1989, the Energy Act 2023, the Data (Use and Access) Act 2025, the ESQCR 2002

The statutory cluster holds the parent instruments under which every other GB energy vocabulary is held. Four Acts and one statutory instrument carry most of the weight in May 2026. The Electricity Act 1989 created the four licence types (generation, transmission, distribution, supply) under Section 6(1) and remains the statutory parent of every other instrument the workspace cites.² The Utilities Act 2000 reorganised regulation and created the Gas and Electricity Markets Authority. The Energy Act 2013 introduced the Electricity Market Reform and the Capacity Market. The Energy Act 2023 created the National Energy System Operator and brought the GB system into its current institutional shape; it also brought the Energy Data Sharing Infrastructure into legal effect. The Data (Use and Access) Act 2025 is the newest of the parents; its first commencement orders brought Section 138 (smart-data schemes) and the bulk of Part 5 (data protection) into force on 5 and 6 February 2026.^{3 4 5}

The ESQCR 2002 (the Electricity Safety, Quality and Continuity Regulations) is the statutory instrument that holds the headline limits at the low-voltage service: regulation 27 fixes the supply voltage at 230 volts plus 10 percent or minus 6 percent on a single phase, and 400 volts on three phases with the same envelope. The dictionary entries in this cluster are short on definition and long on the chain of references because the parent instrument is itself the definition. A reader searching for "Section 6 of the Electricity Act" lands on the entry that names the four licence types and points at Ofgem's role as the licensing authority; the entry then points at the Standard Licence Conditions cluster for the operational detail. The full text of every Act sits on legislation.gov.uk so the dictionary entry carries the section reference rather than reproducing the statutory text.

Licence terms: SLC 25.2, the industry codes, the Distribution Code and the Grid Code

The licence cluster holds the Standard Licence Conditions and the industry codes that the four Ofgem-issued licence types refer to. SLC 25 of the Electricity Distribution Licence is the condition that holds the Long Term Development Statement obligation; SLC 25.2 specifically requires every distribution licensee to publish an LTDS at intervals of not more than seven years, and authorises Ofgem to give directions on the content and the form.¹ The Distribution Code, the Grid Code, the Connection and Use of System Code (CUSC), the Balancing and Settlement Code (BSC), the Retail Energy Code (REC), the Smart Energy Code (SEC), the Uniform Network Code (UNC), and the System Operator Transmission Owner Code (STC) are the industry codes that hold the operational, commercial, and settlement rules referenced by the licence conditions.

The Distribution Code is at Issue 59 (24 April 2026) and the Grid Code is at Issue 6 Revision 37 (13 April 2026); both carry their own change-control panels (the Distribution Code Review Panel and the Grid Code Review Panel) which publish modification reports against the codes.^{7 8} The dictionary entries in the licence cluster are the most cross-referenced on the workspace because every operational rule reaches back to the licence condition that holds it. A reader searching for "DPC4" (the Distribution Code section on operational voltage management) lands on the entry that names the section and points at the Code itself, the licensee category that operates under the Code (every Distribution Network Operator), the Engineering Recommendations the Code refers to (G98 and G99 for connection-stage requirements, G5/5 for harmonics, P29 for voltage unbalance), and the parent Standard Licence Condition that holds the Code in the licence. The chain runs from the operational rule back to Section 6 of the Electricity Act 1989 in four hops.

Data-layer terms: LTDS, CIM, CGMES, SHACL, RDFS and the BSI Engagement Hub

The data-layer cluster is the youngest and the fastest-changing of the five. The Long Term Development Statement (LTDS) is the publication; the Common Information Model (CIM) is the underlying data standard; CGMES v3 is the European profile family the GB regime has adopted under the 2024 Ofgem Direction; the Equipment profile (EQ), the System Capacity profile (SYSCAP), the Steady State Hypothesis profile (SSH), the Topology profile (TP), the State Variables profile (SV), the Short Circuit Results profile (SCR), and the Header profile are the named CGMES application profiles the LTDS uses.¹⁵ The Shape Constraint Language (SHACL) is the W3C language used to constrain the profile shapes; the Resource Description Framework Schema (RDFS) is the underlying schema language; the BSI CIM Engagement Hub is the official location of record for the LTDS data-exchange definition artefacts confirmed in the third derogation letter of 13 May 2026.^{6 17}

The dictionary entries in the data-layer cluster carry the most technical detail because the underlying standards are recent in the GB regime and the vocabulary is not yet widely shared. The IEC 61970-301 standard is the parent of the CIM base model and the source of the canonical class names (ConductingEquipment, EquivalentInjection, ACLineSegment) the LTDS profiles refer to.¹² The IEC 61968-13 standard adds the distribution-management extensions (the classes specific to medium-voltage and low-voltage assets) that the GB distribution licensees use.¹³ CGMES v3 is the application profile family that fits the IEC base into the European data-exchange framework.¹⁴ The Grid Code modification GC0139 is the live modification (with the Authority for decision as of April 2026) that brings the GB Grid Code into line with the CGMES v3 directive Ofgem issued in 2024.¹⁶ A reader searching for "CGMES" lands on the entry that names the standard, points at IEC 61970-301 as the parent, points at the seven application profiles as the constituent vocabulary, and points at GC0139 as the live regulatory change.

Network terms: GSP, BSP, ANM, P29 and the voltage-tier shorthand

The network cluster holds the operational vocabulary used by transmission and distribution licensees. Grid Supply Point (GSP) is the 132 kilovolt boundary substation where the transmission network meets the distribution network; Bulk Supply Point (BSP) is the next step down (typically 132 to 33 kilovolts); the primary substation is the next step (typically 33 to 11 kilovolts); the secondary substation is the last step (typically 11 to 0.4 kilovolts). Active Network Management (ANM) is the operational pattern under which a Distribution Network Operator monitors local voltage and curtails or releases connected generators and demand to keep the voltage envelope inside the operational limit.

The Engineering Recommendations carry their own vocabulary. G98 Issue 2 (10 March 2025) sets the connection requirements for micro-generation up to 16 amperes per phase; G99 Issue 2 (10 March 2025) sets the requirements for everything larger up to transmission-connected generators (the Types A, B, C and D introduced by the European Network Code on Requirements for Generators).^{9 10} G5/5 (June 2020) sets the harmonic compatibility limits at every voltage. P29 (Issue 1, 1990; revision in progress through the Distribution Code Review Panel) sets the voltage unbalance limits at 2 percent at 132 kilovolts and below, with up to 1.33 percent allocatable to a single customer.¹¹ The voltage-tier shorthand (EHV for extra-high voltage at 132 kilovolts and above; HV for high voltage at 1 kilovolt to 132 kilovolts; LV for low voltage below 1 kilovolt) carries the regulatory boundary between Ofgem's transmission and distribution licence types and is used in the colour coding on the workspace diagrams.

Market terms: BMRS, capacity market, contracts for difference, MHHS and settlement

The markets cluster holds the commercial vocabulary of the GB wholesale and capacity markets. The Balancing Mechanism Reporting Service (BMRS) is the NESO-operated portal that publishes the half-hourly system data used by every market participant; the Capacity Market (CM) is the auction-based mechanism that procures dispatchable capacity for delivery several years ahead; Contracts for Difference (CfD) are the strike-price agreements the Low Carbon Contracts Company holds with low-carbon generators awarded in Allocation Rounds (AR1 to AR7 to date).^{18 19}

The settlement vocabulary sits inside the Balancing and Settlement Code which Elexon administers. Market-wide Half Hourly Settlement (MHHS) is the programme migrating GB settlement from the existing profile classes to half-hourly data for every meter; BSC modification P408 is the regulatory change that authorises the migration; the milestones M10 to M13 in early 2026 marked the first 10 million Meter Point Administration Number (MPAN) initiations; full implementation is Milestone 15 in May 2027; cutover is Milestone 16 in July 2027.^{20 21} The Meter Point Administration Number (MPAN) is the 13-digit identifier for an electricity supply point; the Meter Point Reference Number (MPRN) is the parallel identifier for a gas supply point. A reader searching for "MHHS" lands on the entry that names the programme, points at BSC P408 as the regulatory change, names the milestones, and points at the supplier-licensee category and the meter-operator licensee category that share the migration obligation.

Using the dictionary in practice when reading paperwork

The dictionary is the second tool to reach for when reading a fresh Ofgem consultation or a NESO publication. The first tool is the inline tooltip glossary on the workspace pages, which gives a one-line definition next to the acronym in the running prose. The tooltip is the version of a definition that does not break the reading flow. When the tooltip is enough the reader keeps going; when it is not, the dictionary entry gives the full two-paragraph reading and the citation pointer to the parent instrument. The same applies in reverse when drafting: a draft note carries tooltip-length annotations next to acronyms, and the longer dictionary entries take care of the readers who need to settle a disputed reading.

Every dictionary entry resolves to one of the primary sources below, recorded with the exact wording quoted from the source where it is available. When a reader queries a definition the first thing to check is that source: is the quoted wording still current, has the source published a newer version, has the date of the last check slipped too far behind. If the answer to any of those is yes, the entry is updated against the new source and the check date is reset.

The fourth tool is the workspace itself. The dictionary cross-references point at the workspace pages that hold the long-form treatment of a topic: the LTDS entry points at the dedicated LTDS page; the SLC 25.2 entry points at the governance page; the CGMES entry points at the data-and-standards architecture page. The reader who wants more than the dictionary entry can carry on to the workspace page; the reader who has all they need stops at the dictionary entry. The two reading modes are connected so a reader can move between them without leaving the workspace.

The pattern of use that has emerged from twelve months of running the dictionary is this. A search starts from a term read in a fresh piece of paperwork. The dictionary entry gives what the term means and points at the parent instrument. The parent instrument is then opened at the section the entry cites. The workspace page that covers the topic the term sits inside supplies the connective tissue between the term and its neighbours. The round trip takes ninety seconds for a familiar term and ten minutes for an unfamiliar one. The discipline of grounding every entry in a primary source means entries rarely have to be revised under pressure; the entries that move are the ones whose parent instrument has itself moved, and the manifest records the date of the move.