Red Arrows over London - if an engine failure
To answer a comment a bit further back about a possible engine failure over London - as single engine aircraft are not normally allowed to fly over London.
Few years ago a pilot from the Battle of Brittan Memorial Flight said in a TV documentary if they had an engine failure when doing a fly-past over Buckingham Palace, etc, they would 'bite the bullet and go in the Thames'.
He didn't say they had 'orders', from his tone it was just the accepted thing to do.