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On 15 April 2025, Ofgem confirmed approval of the National Energy System Operator’s (NESO) methodologies for reforming the electricity transmission connections process. NESO have subsequently published a final suite of connection methodologies. The reforms (known as TM04+) aim to prioritize projects that are both “ready” and “needed” for the energy transition, moving away from the “first come, first served” approach.
Background
In December 2024, NESO submitted a reform package to Ofgem, proposing structural changes to the connections framework. Its goal was to ensure the mix of transmission projects aligns with Great Britain’s Clean Power needs by 2030. This package introduced three core methodologies, which were developed to work alongside revised industry codes and licence modifications:
- Gate 2 Criteria Methodology which defines the eligibility and evidence required for projects to progress through the Gate 2 stage of the transmission connections process.
- Connections Network Design Methodology (CNDM) which explains how the transmission network will be planned and designed to accommodate projects in the reformed connections queue (including capacity assessments and design principles).
- Project Designation Methodology which establishes how projects will be categorised and prioritised within the connections queue (based on national energy goals and readiness criteria).
Following a consultation process launched by Ofgem in February 2025, NESO published updated versions of the methodologies on 21 March 2025.
Ofgem approval and final updates
Ofgem’s decision on 15 April 2025 formally approved the methodologies with a few recommended refinements. NESO responded by publishing a final suite of changes in April 2025. These changes included:
- Removal of references to “the Pause” (which related to NESO’s pause in accepting new transmission connection applications) which is now redundant due to Ofgem’s decision to adopt alternative process routes.
- Protection Clause assurance that developers with projects due to connect by 31 December 2027 will retain their existing connection dates and connection points.
- Protection Clause assurance for projects that submitted planning by 20 December 2024 but have not yet received planning consent, that they may still be eligible to receive Gate 2 terms in future application windows (even if zonal capacity limits are breached).
- Alignment with Government policy to reflect the April 2025 update to the Clean Power 2030 Action Plan.
Next steps
The new methodologies will underpin the forthcoming ‘Gate 2 to Whole Queue’ process, expected to commence in July 2025 for transmission customers. Distribution customers will begin the process earlier, from May 2025, via their respective DNOs or transmission-connected IDNOs.
Importantly, NESO anticipates using these finalised methodologies in the first enduring application window, currently expected to open by the end of 2025. However, further refinements may follow based on lessons learned during implementation.
Implications for developers
These changes significantly impact how new and existing projects interact with the grid connection process. We recommend that developers review the finalised methodologies carefully to understand eligibility, prioritisation, and timing.
If you are a developer and would like support in navigating the implementation of TMO4+, please contact a member of our team.
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