Thanks for the link, I didn't know very much about how this is implemented and now it's much clearer. I fully expect to see the same things I've just learned on a Youtube video or cable TV news some time from now when stuff goes badly wrong and it doesn't mesh with the simple "Huge metal tank somewhere" picture of such a reserve I'd imagine the average voter has.

Like Britain's ageing gas mains this feels like a measure which should have become irrelevant just as it would otherwise need renewing, a huge saving - but of course we (as a species) will always procrastinate so that was never going to happen. For the next 5-10 years Britain will continue replacing pipelines to deliver a fossil fuel (natural gas, methane, for heating) we should have long since stopped using but didn't.