Ofgem approves P511, barring large generators from the VTP wholesale market route built for consumer flexibility

Ofgem has approved Balancing and Settlement Code modification P511, closing off the P415 Virtual Trading Party (VTP) wholesale market route to large-scale generation assets^[1]. The decision ends a dispute that had been escalating since at least September 2025, when data showed that approximately £19 million of supplier compensation cashflow had been mutualised in the six months to 28 February 2026 - a cost ultimately borne across the supplier base.

What P415 was built to do - and what went wrong

P415, approved by Ofgem in October 2023, created the VTP role to give independent aggregators a route to trade consumer-led flexibility - domestic demand response, small behind-the-meter assets - in the wholesale market. The mechanism came with a mutualised compensation fund: suppliers whose imbalance positions were affected by VTP actions were compensated through a shared pot.

The problem that prompted P511 was straightforward. P415 was introduced to facilitate wholesale market access for consumer-led flexibility and smaller behind-the-meter assets via the VTP route, but evidence showed that large-scale generation assets, which already had established routes to market, were using the mechanism in a way that was not originally intended - leading to increasing mutualised supplier compensation cashflows, a risk of double remuneration for certain assets, and distortion of the market signals intended to support consumer-led flexibility.

The increase in the mutualised compensation fund appeared to originate from large generators using VTP arrangements, creating a risk that certain generation assets could be paid both by their VTP and their power offtaker - with unintended consequences for market signals and efficiency.

The P511 fix: a Trading Eligibility Threshold

P511 proposes introducing a trading eligibility threshold, above which generation assets would be ineligible to participate in the wholesale market via Virtual Trading Parties. The modification defines a new category - "ineligible secondary trading BM units" - in the BSC code.

Critically, the restriction is narrow in scope:

• Generation assets above the threshold lose access to the VTP wholesale market route only
• Those assets retain access to the wholesale market through existing routes and can continue to participate in the balancing mechanism and ancillary services
• Smaller assets and genuine consumer-led flexibility remain eligible to use the P415 VTP mechanism as originally designed

How the modification reached Ofgem

Axle Energy raised P511 on 17 March 2026 and proposed it for an urgent timetable. The BSC Panel considered the modification at an ad-hoc meeting on 18 March before recommending urgency to Ofgem, which granted it on 31 March 2026.

The workgroup process ran through four meetings between April and June 2026. Twenty-eight responses were received to the P511 Urgent Modification Consultation. The consultation was not without dissent: some respondents argued that the threshold-based eligibility criteria were arbitrary and that the modification risked distorting competition. Others supported it as a necessary interim fix to restore market integrity.

Elexon presented the P511 Draft Urgent Modification Report to the BSC Panel at its meeting on 11 June 2026. The Panel considered workgroup views and consultation responses, noting the compressed urgent timeline and the need to address material ongoing financial impacts promptly. Members discussed concerns around the depth of analysis, potential impacts on competition, and implementation lead times, and agreed that the implementation date should be amended from 5 working days to 10 working days following the Authority's decision. Following the Panel's recommendation that P511 should be approved, the Final Urgent Modification Report was sent to Ofgem for decision.

What to watch

P511 is explicitly framed by some respondents as an interim measure. The threshold-based approach resolves the immediate cost problem but does not redesign the underlying compensation architecture - that work falls to companion modifications P509 and P510, which are still in progress. Ofgem's willingness to approve P511 on an urgent basis, despite objections about analytical depth, signals that the regulator views the mutualised cost exposure as a live consumer-detriment issue that cannot wait for a more comprehensive solution. Implementation is due 10 working days after the decision date.