Okay I admit that was a pretty bad example.
Here's another one. Say for example there was a massive tsunami that hit London, who do you think will get evacuated first?
Well that example is pretty wild as well. No tsunami will hit London - it's in the completely wrong place + orientation relative to the undersea tectonic plates. And if there was a tsunami that was so large as to wash up over southern England and reach London - the world's probably about to end
A better example I think is a terrorist attack on London. And honestly I don't think the Queen will be the first to go into hiding. Her parents stayed the war in London, and she'd want to live up to that at the very least. But she is also a tough old bird and various reports say that she is very much concerned for the welfare of her people, and I really don't think she'd leave. A captain goes down with their ship and all that.
Now if we're talking about any POTUS - well that's a completely different story (somewhat joking - but I don't think the president would have any choice in the matter - the Secret Service/Marine One/Air Force One etc probably wouldn't stop even if he demanded it...).
(Also out of curiosity - does anyone know if 32 Sqn do evacuations of Royals and government officials like Marine One does for the president?)