UK Emergency Procedures In The Event of Nuclear War etc..

Good post OP.

All sounds pretty plausible to me. I can't see any dignitaries being flown anywhere in the event of something like this, way too risky. It would be deep underground all the way, best chance of avoiding being vapourised.

The thing is, your talking underground and you don't need a mountain to be underground, close by me is RGHQ6.1 which is set under the Downland hills..

RGHQ6.1 was to be the seat of Government for South Eastern England if a nuclear strike occurred, it includes a ministers suit, BBC studio and was an underground blackops base stretching back to WW2.

That nuclear bunker is now (ROFL) a underground police training centre. As if the local police need to train in a nuclear bunker..

[link to www.thetimechamber.co.uk]

I am sure the government have multiple directions to travel depending on the threat.. but in my opinion, mountains are not required.

There are,(were) six underground sites designated as "Regional seats of government" which could be used in the event of nuclear war. Not surprisingly there were sited equip-distant around London about 30-40 miles from the city.

For your information the Victoria line, nor any other underground line passes under Buckingham palace or Downing Street, though there is a private underground walkway from Downing street to the houses of Parliament, which is next to Westminster underground station.