MHHS reverse migration: what it is, and what happens when it ends

What reverse migration actually is

Market wide half hourly settlement moves every meter point from profiled settlement onto settlement using actual half hourly data. That move is the migration. Reverse migration is the fallback built into the transition: if a meter point is migrated and something is wrong, the data, the flows or the settlement result, it can be returned to the old arrangements while the problem is fixed. Think of it as the undo button for the programme, and like most undo buttons it is only there for a limited time.

Why the 28 October deadline matters here

M14 on 28 October 2026 is the point at which reverse migration ends. After that date a migrated meter point cannot go back to the old regime. If your data quality or settlement position is wrong, you no longer roll back and regroup, you fix it forward, live, under the new arrangements. That is a materially different risk. Before M14 a mistake is recoverable. After M14 the same mistake sits in your settlement and, from M16 on 2 July 2027, surfaces on a four month clock rather than a fourteen month one.

Who should be paying attention

Any supplier or agent still migrating, and in particular anyone migrating late. The later you migrate, the less runway you have to spot a problem and use reverse migration before the window shuts. It also matters to anyone who is technically migrated but not confident in their data quality, because the value of the safety valve is only realised if you know you have a problem while you can still act on it. Meter operators, data collectors and aggregators sit inside this too, because a data issue at the agent end is exactly the kind of thing reverse migration exists to catch.

What to do while the window is open

Treat the time before 28 October as the period in which mistakes are still cheap. Get an honest read of your migration and data position now, not a project plan status but a real check of whether your flows and settlement result would survive scrutiny this week. Where there is doubt, the point of reverse migration is to use it deliberately rather than discover you needed it after it has gone. And if you are not yet migrated, build the plan on the assumption that anything pushed through in the final weeks carries less margin for recovery than anything done earlier.

The honest summary

Reverse migration is not a detail, it is your last line of defence during the transition, and it expires on 28 October. The suppliers and agents who come out of this well are the ones who find their problems while they can still be undone.

Milestone dates are from the MHHS Programme’s published plan. This article is guidance, not regulatory advice.