[implements]

> I suspect you will find its not a single point of failure either. It’s just that Hayes is a high-demand area, so see above for lack of excess capacity .... if one site goes boom, the other will struggle to take on 100% load.

Hayes (North Hyde) is a few miles NE of Heathrow, but Laleham (similar sized) is only a few miles South - I’d would have assumed both served as fully redundant supplies for the airport, given it’s critical national infrastructure.

(The old BBC Television Centre in London had three independent supplies, I believe)

[ben_w]

> (The old BBC Television Centre in London had three independent supplies, I believe)

There's a story, possibly apocryphal, that the UK nuclear deterrent submarines used the continued broadcast of Radio 4 as a dead-man switch to determine if nuclear war had broken out and they needed to open the safe containing their orders.

Which is to say: What counts as "critical national infrastructure" can be surprising.

[implements]

Radio 4 on long wave, I believe - which is only guaranteed until the end of June this year because the BBC’s stock of irreplaceable high power valves is running out. As well as triggering Armageddon the LW signal also switched older electricity meters (phew, back on topic!) between standard daytime and cheap overnight power.