P487 Balancing and Settlement Code (BSC) proposed changes

What changed

Ofgem approved BSC Modification P487, which makes the M15 MHHS migration deadline contractually enforceable. From M15 (7 May 2027), any supplier that has not completed migration of its MPANs into the new market-wide half-hourly settlement arrangements is barred from registering new customers until it does. The restriction is suspended only if the MHHS Senior Responsible Owner grants that supplier an exemption, with an associated appeals process to be set out in the MHHS Migration Framework. The modification takes effect on the date the Framework changes are implemented, or 25 June 2026, whichever is earlier, so the rule is live well over a year before the deadline it enforces.

The load-bearing fact is procedural, not technical. The BSC Panel recommended on 11 December 2025 that Ofgem reject P487. Ofgem overrode that recommendation, citing BSC Applicable Objectives (c) and (d) and its own assessment of the modification's impact on competition and consumers, informed by the MHHS Programme's February 2026 "Troublesome MPANs" information request. Panel overrides are rare. This one signals that Ofgem has decided MHHS delivery risk now outweighs the competition concerns the Panel weighed more heavily, and that it is willing to spend institutional capital to say so.

What this means in practice

The mechanism is a growth ban. A supplier that misses M15 keeps its existing book but cannot acquire a single new customer until it finishes migrating. For a challenger supplier whose business case depends on net customer growth, that is not a fine; it is a freeze on the revenue line that services its cost base and its investors. The cost falls hardest on exactly the participants least able to absorb a migration programme: smaller suppliers with thinner IT functions and less ability to throw resource at a fixed-date data exercise. Larger incumbents with mature settlement operations face a deadline; challengers face an existential one. This is a structural feature of the design, not a side effect.

The exemption pathway is where the real action will be. Exemptions are granted at the discretion of the MHHS SRO, against guidance on circumstances in which they "would and would not be likely to be issued." Discretionary relief from a binding cost is an invitation to apply for it, and the suppliers with the strongest incentive to apply are precisely those most exposed to the ban. Expect heavy use, contested refusals, and pressure on the appeals process. The guidance the SRO writes, not the BSC text Ofgem just approved, will determine how hard this stick actually hits. A permissive exemption regime turns P487 into a paper threat; a strict one turns it into the binding constraint Ofgem intends. That document is not yet consulted on.

The "Troublesome MPANs" request matters here. Some MPANs cannot be migrated cleanly for reasons outside any single supplier's control: data defects, metering edge cases, third-party dependencies. Ofgem's reference to that work signals it is aware the deadline interacts with problems suppliers cannot unilaterally fix, which is the obvious ground on which exemption claims and appeals will be fought. The line between "supplier failed to deliver" and "supplier was defeated by a defective MPAN it did not create" is where the litigation-by-governance will sit.

The substantive shift is in posture. The April 2025 joint letter from the Secretary of State and Ofgem's CEO was an instruction without a consequence attached. P487 attaches the consequence. MHHS has slipped repeatedly, and every slip has carried the cost of running legacy and new settlement systems in parallel and deferring the more accurate, half-hourly price signals the programme is supposed to unlock. P487 is the point at which "do not delay further" stops being an exhortation and becomes a contractual penalty with a named victim: the non-migrating supplier's growth pipeline.

What happens next

The immediate gating item is the MHHS Migration Framework update. Ofgem expects the MHHS Programme to consult on the exemption and appeals process "as soon as possible," substantially on the documentation already put to the BSC Panel in December 2025. That consultation, run under MHHS Programme Change Request governance rather than the BSC modification process, is the one to watch: it sets the exemption criteria that decide whether P487 bites. Suppliers and their advisers should engage with it directly rather than treating the Ofgem decision as the settled position.

P487 itself takes effect on Framework implementation or 25 June 2026, whichever is earlier. The enforced deadline, M15, remains 7 May 2027, after which legacy settlement systems can be retired once the final legacy settlement date is reconciled. Between June 2026 and May 2027 the operative questions are: how many suppliers credibly forecast missing M15, what the exemption guidance ends up saying, and whether any supplier tests the appeals route before the deadline rather than after. Watch for the MHHS Programme consultation publication, the final exemption guidance, and any subsequent BSC modification that adjusts the mechanism if a wave of exemption applications reveals the M15 date is not achievable for a material slice of the market.