43 groups own 87 per cent of Britain's operating battery capacity

46 batteries, 1,019 MW, where no document names the owner yet

The honest state of the rest. Some are project companies waiting on a single filing. Some name nobody at all in either register, and the site itself has to be identified before the company can be. A prefix on a unit code is not evidence: eleven units carry a code that looks like one operator's and the only one the register names belongs to somebody else.

How the owner is decided

A control filing decides it. Companies House publishes, for every company, who holds more than a quarter of it and who can appoint and remove its directors. We follow that chain up from the project company until it stops and record where it stopped. Everything else is a lead to be checked against one: a capacity market site a few hundred metres from an ownerless unit, a second phase at the same postcode, a company's previous names, the initials in a balancing code. Shared directors and shared registered offices are not evidence, because both survive a sale. The finding says why the registers cannot answer this question, and the optimiser pages are the other half of it: who sells.