Constraint Management Intertrip Service | National Energy System Operator
Summary
NESO's Constraint Management Intertrip Service (CMIS) page consolidates the three active constraint management programmes: EC5 East Anglia (enduring service starting mid-2026), B6 Anglo-Scottish boundary (15 generators contracted, now extended to September 2027), and a new CMIS Scotland consultation launched 13 April 2026. These are commercial alternatives to transmission build, paying generators to accept automatic disconnection post-fault so more power can flow on existing infrastructure pre-fault.
Why it matters
This is the right direction: pricing constraint solutions through competitive tender rather than defaulting to network build. The B6 contract extension to 2027 signals NESO still lacks a permanent solution for Scottish constraints, meaning curtailment costs continue to fall on consumers via BSUoS. The Scotland consultation is the one to watch, as it extends the intertrip model further north where constraint costs are highest.
Key facts
- •B6 CMP 2024-25 contracts awarded to 15 generators, now extended to 30 September 2027
- •CMIS EC5-Enduring service to begin mid-2026, replacing interim contracts
- •CMIS Scotland consultation and EOI launched 13 April 2026
- •EC5-Enduring tender result published 18 June 2025
- •B6 manages the Anglo-Scottish boundary constraint; EC5 manages East Anglian congestion
Timeline
Areas affected
Related programmes
Memo
What this is about
NESO's Constraint Management Intertrip Service (CMIS) is the mechanism for buying constraint relief commercially rather than building new transmission lines. The concept is straightforward: pay generators to accept automatic disconnection after a fault occurs, so that more power can flow on existing infrastructure before a fault. This lets NESO operate transmission lines closer to their thermal limits, reducing the volume of generation curtailed pre-emptively.
This page consolidates three active CMIS programmes covering East Anglia, the Anglo-Scottish boundary, and a new Scottish expansion. Together they represent NESO's primary commercial toolkit for managing the transmission constraints that currently cost consumers over £1bn annually through Balancing Services Use of System (BSUoS) charges.
Key points
EC5 East Anglia: enduring service from mid-2026. The East Anglia region has significant offshore wind capacity constrained by onshore transmission limits. NESO ran interim CMIS contracts from 2023 and completed the enduring tender in June 2025. The enduring service links generators across East Anglia to the East Anglia Operational Tripping Scheme (EAOTS), allowing the Energy National Control Centre to push more power through existing circuits. This transitions from stopgap contracts to a permanent commercial arrangement.
B6 Anglo-Scottish boundary: 15 generators contracted, extended to September 2027. The B6 boundary between England and Scotland is the most constrained point on the GB transmission system. Fifteen generators won contracts through the 2024-25 tender process. The critical development is the contract extension: these were originally due to expire in October 2025 but have now been pushed to 30 September 2027. NESO states this is to allow "adequate time to build the correct and optimal CMIS solution for this region's network." In practice, this means the underlying constraint problem is not going away, and NESO does not yet have a successor arrangement ready. Every month these contracts run, the cost flows through to BSUoS.
CMIS Scotland: consultation launched 13 April 2026. This is the new development. NESO is extending the intertrip model further north into Scotland, beyond the B6 boundary. Six documents were published on 13 April: a consultation and expression of interest letter, draft service specification, draft service terms, draft framework agreement, EOI submission proforma, and a query log. This is a combined consultation and EOI process, meaning NESO is simultaneously seeking industry feedback on the design and identifying potential providers.
The commercial model. CMIS operates through competitive tender. Generators submit proposals, which are assessed for technical feasibility by the relevant Transmission Owner, then evaluated against commercial criteria. Successful providers enter framework agreements with standard contract terms. The service specification defines what capability is required; the commercial assessment determines what NESO pays. This is a bilateral contract model, not a market mechanism, but it does introduce price discovery through competition.
What CMIS does and does not solve. Intertrip services reduce pre-fault curtailment costs by allowing higher power flows on existing lines. They do not increase the physical capacity of the transmission network. They are an operational efficiency measure that buys time while transmission reinforcement proceeds. The B6 extension to 2027 illustrates the tension: CMIS keeps costs lower than they would otherwise be, but the constraint itself persists until new infrastructure (principally the Eastern HVDC link) is commissioned. The saving is relative to a counterfactual of unconstrained curtailment, not an absolute reduction in system costs.
What happens next
CMIS Scotland consultation is open now. The publication date of the EOI documents was 13 April 2026; closing dates for responses should be in the consultation letter. Generators in Scotland with the technical capability to provide post-fault tripping should be reviewing the draft service specification.
EC5 enduring service transitions from interim to enduring contracts mid-2026. Providers are already contracted following the June 2025 tender result.
B6 contracts run to 30 September 2027. NESO will need to decide well before that date whether to retender, extend again, or replace with a different constraint management approach. The language about building an "optimal CMIS solution for this region" suggests a retender under revised terms is more likely than a further extension, but no timeline has been published.
The wider context is NESO's Constraint Management Strategy. CMIS sits alongside network reinforcement, commercial intertrips, and the Connections Reform programme. As constraint costs continue to rise with increasing renewable penetration, the commercial alternatives to transmission build become more important, and the question of whether bilateral tenders or a more market-based approach would deliver better price discovery becomes harder to defer.
Source text
Constraint Management Intertrip Service | National Energy System Operator Show/Hide Menu Toggle Add to favourites Close tooltip Sign in to add this page to your favourites Sign in or register Show favourites Close Close tooltip Sign in or register to manage your favourites Sign in or register Help You are now signed in Visit My NESO account to view and manage your dataset subscriptions. Maybe later Go to your account Constraint Management Intertrip Service The Constraint Management Intertrip Service (CMIS) looks for ways to reduce the cost of managing constraints at various locations on the electricity system. The Future Energy Scenarios (FES) and Electricity Ten Year Statement (ETYS) have shown that changes in the volume and location of electricity generation will lead to significant constraint costs if nothing is done. Our first step is to carry out detailed analysis to determine future constraint requirements which will be informed by changes to the generation mix and demand profile. We will then seek solutions through CMIS tenders for capability that can reduce the cost and volume to manage constraints. Contracted solutions will then be considered alongside other tools in managing constraints in real-time. What we’re trying to achieve EC5 Constraint Management Intertrip Service CMP B6 Scotland updates CMIS Scotland What we’re trying to achieve Reducing the need for build solutions Reducing the cost of managing constraints means we can mitigate the consequences of unplanned events (post-fault constraint management services), which could help reduce the need for build solutions. Seeking services from new providers Constraint service providers are vital to meeting system needs. We’re looking for new providers to help us reduce constraint costs on the electricity system. We’ll invite potential providers and relevant network owners to submit proposals that address specific system needs. This is a collaborative process between providers, NESO and the relevant network operators, assessing the proposal’s feasibility and commercial value. Following technical and economic assessment we will recommend solutions to move forward either via commercial contracts or regulated arrangements. Key Documents Past Event Materials RFI Documents Key Documents Name Key Documents Documents and materials Name Constraint Management Stakeholder Engagement Webinar Name Constraint Management Pathfinder RFI Pack EC5 Constraint Management Intertrip Service The EC5 Constraint Management Intertrip Service (CMIS) aims to reduce network congestion costs in the East Anglian (EC5) region by building post-fault intertrip links between generation across the East Anglia region and the East Anglia Operational Tripping Scheme (EAOTS). By doing so, the ENCC can facilitate more power to flow on the existing transmission infrastructure pre-fault, thus reducing the amount of generation being curtailed pre-emptively when the expected flow exceeds the current capability of the circuits. NESO have launched a market-wide tender, that will now aim to contract for a CMIS EC5-Enduring service to begin in mid-2026. The project team previously identified that there was a value opportunity to begin the service early, i.e. set up ‘interim’ contracts, and these will run until mid-2026, from which point the CMIS EC5-Enduring service will then begin. CMIS workshop - 16 March 2023 EC5 CMIS interim documents CMIS EC5-Enduring documents Rich text Webinar recording part 1 Webinar recording part 2 Name CMIS webinar 16 March 2023 FAQs CMIS webinar 16 March 2023 slide pack EC5 CMIS interim consultation and CMIS webinar feedback Name Published 2. Consultation and Webinar Feedback 3 May 2023 1. Consultation and Webinar Feedback Letter 3 May 2023 EC5 CMIS interim documents Name Published 3. Draft Standard Contract Terms (now outdated, not for use) 6 Mar 2023 4. Consultation Feedback Form 6 Mar 2023 2. EC5 Interim Consultation Presentation 6 Mar 2023 1. EC5 Interim Consultation Letter 6 Mar 2023 EC5 CMIS interim tender documents Name Published 2. EC5 CMIS interim submission proforma 26 May 2023 4. Comparison standard contract terms (updated 03 July 2023) 26 May 2023 3. Final standard contract terms (updated 03 July 2023) 26 May 2023 5. EC5 CMIS query form 26 May 2023 1. EC5 CMIS interim ITT letter 26 May 2023 6. External general tender query (TQ) log 5 Mar 2023 7. National Grid safety policy 4 Mar 2023 EC5 CMIS interim - tender outcome Name Published EC5 interim result summary letter 29 Jan 2024 CMIS EC5-Enduring Tender Result Name Published 1. CMIS EC5-Enduring Tender Result Summary Letter 18th Jun 2025 CMIS EC5-Enduring consultation webinar Name Published 1. CMIS EC5-Enduring webinar recording 28 Nov 2023 2. CMIS EC5-Enduring consultation webinar slides 28 Nov 2023 3. CMIS EC5-Enduring consultation webinar Q&A log 28 Nov 2023 CMIS EC5-Enduring documents Rich text Name Published 1. CMIS EC5-Enduring Consultation Letter 2 Nov 2023 2. CMIS EC5-Enduring Consultation Presentation 2 Nov 2023 3.CMIS EC5-Enduring Service Specification 2 Nov 2023 4. Draft Framework Agreement 2 Nov 2023 5. Draft Standard Contract Terms 2 Nov 2023 6. Consultation Feedback Form 2 Nov 2023 7. Consultation - Industry feedback and responses 10 Jan 2024 CMIS EC5-Enduring expression of interest documents Rich text Name PublishedSort ascending 1. CMIS EC5-Enduring - EOI letter 22 Jan 2024 2. CMIS EC5-Enduring - EOI submission proforma 22 Jan 2024 3. CMIS EC5-Enduring - EOI service terms 22 Jan 2024 4. CMIS EC5-Enduring - EOI presentation 22 Jan 2024 5. CMIS EC5-Enduring - framework agreement 22 Jan 2024 6. CMIS EC5-Enduring - service specification 22 Jan 2024 7. EC5-Enduring SCTs v20 against v16 (consultation) 22 Jan 2024 CMP B6 Scotland updates One of the key areas of congestion currently on the system is the Anglo-Scottish boundary (B6) which is limited by a constraint, and therefore sometimes requires renewable generation to be turned down pre-fault. During times of network congestion, we take action to reduce generation pre-fault which can lead to higher constraint costs even though the likelihood of a network fault is very low. We are aiming to reduce the impact of network constraints, maximise renewable generation on the system and lower costs for the end consumer. The B6 Constraint Management Pathfinder (CMP) 2024-25 Tender has concluded Contracts have been successfully awarded to 15 generators for the B6 CMP 2024-25 service delivery, the results of the tender can be viewed below. Following a consultation on documents relating to the B6 Constraint Management Pathfinder (CMP) 2024-25 service, an Expression of Interest was launched. Successful EOI submissions were assessed for feasibility by the relevant Transmission Owners, and technically feasible parties then had the opportunity to participate within the tender period. They were then assessed against the criteria set out in the Service Specification, and contracts were subsequently awarded to the successful parties. B6 CMP 2024-25 The documents below are for the current B6 CMP for service delivery September 2024 - October 2025. Since these contracts were awarded, NESO have been continuing to investigate optimal solutions for both the B6 boundary as well as the surrounding boundaries, particularly further north into Scotland as we move forward. To ensure there is adequate time to build the correct and optimal CMIS solution for this region’s network, a decision has been taken to extend these current contracts. These contracts have now been extended until 30 September 2027. B6 CMP 2024-25 Results B6 CMP 2024-25 Invitation to Tender Documents B6 CMP 2024-25 Expression of Interest Documents B6 CMP 2024-25 FAQs B6 CMP 2024-25 Consultation Documents Rich text These are the results from the B6 CMP 2024-25 tender process. Any queries please email: [email protected] Name B6 CMP 2024-25 Results Summary Letter 25.11.22 B6 CMP 2024-25 Results B6 CMP 2024-25 Invitation to Tender Documents Rich text The Tender Period was open from Monday 8 August 2022 until Friday 16 September 2022. The Tender Documents were released on Monday 8 August 2022. Any queries please email: [email protected] Name 09.09.22 B6 Constraint Management Intertrip Service Standard Contract Terms 09.09.22 Comparison to 08.08.22 B6 CMIS Standard Contract Terms B6 CMP 2024-25 Summary of EOI and Feasibility Studies Results 08.08.22 B6 Constraint Management Intertrip Service Framework Agreement 08.08.2022 B6 Constraint Management Intertrip Service 202425 Comparison of Standard Contract Terms (SCTs) B6 CMP 2024-25 Service Specification B6 CMP 2024-25 Tender Summary Presentation B6 CMP 2024-25 Invitation to Tender Letter B6 CMP 2024-25 Tender Instructions B6 CMP 2024-25 Expression of Interest Documents Rich text The Expression of Interest stage was open from Monday 28 March until Friday 22 April 2022. Any queries please email: [email protected] Name B6 CMP 2024-25 Service Specification B6 CMIS 2024-25 Standard Contract Terms B6 CMP 2024-25 Consultation Feedback Summary B6 CMIS 2024-25 Comparison of Standard Contract Terms B6 CMIS 2024-25 Framework Agreement B6 CMP 2024-25 Expression of Interest Presentation B6 CMP 2024-25 Expression of Interest Proforma B6 CMP 2024-25 Expression of Interest Letter Rich text FAQs published 28 March 2022. Name B6 CMP 2024-25 FAQs B6 CMP 2024-25 Consultation Documents Rich text These documents were consulted on from 7 February 2022 until 25 February 2022. Name CMP B6 Consultation Summary CMP B6 Draft Framework agreement CMP B6 Draft Contract terms CMP B6 Draft Service Spec 2024-25 Archive CMP B6 2023-24 The documents below are from the last year's CMP B6 tender 2023-24. These are uploaded for reference and are not part of this year's B6 CMP 2024-25 service. CMP B6 2023-24 Results CMP B6 2023-24 Commercial Documents CMP B6 2023-24 Contract Documents CMP B6 2023-24 Expression of Interest Documents CMP B6 2023-24 Results Rich text These are the results of the B6 CMP 2023-24. Name CMP B6 2023-24 Industry Results Letter CMP B6 2023-24 Results CMP B6 2023-24 Commercial Documents Name Final B6 Commercial Assessment Methodology CMP B6 2023-24 Contract Documents Name Final contract terms Draft contracts v2 consultation Draft contracts v1 consultation CMP B6 2023-24 Expression of Interest Documents Name Draft Commercial Assessment Methodology CMP FAQ Expression of Interest Submission Template Technical Specification Invitation to EOI letter EOI Pack CMIS Scotland CMIS Scotland - Consultation & Expression of Interest documents Name Published Sort ascending CMIS Scotland - Consultation and Expression of Interest Letter 13 Apr 2026 CMIS Scotland - Consultation & EOI Query Log 13 Apr 2026 CMIS Scotland - Draft Service Specification 13 Apr 2026 CMIS Scotland - EOI Submission Proforma 13 Apr 2026 CMIS Scotland - Draft Service Terms and Conditions 13 Apr 2026 CMIS Scotland - Draft Framework Agreement 13 Apr 2026 Want to stay updated? Email us If you need to get in touch or need further information drop us an email. Sign up for our newsletter Sign up for our newsletter and tick ‘Network Options Assessment’ to get alerts about new requirements. logo--facebook