I cannot see what the big deal is regarding a twin operating low level over central London as long as he is not scud running and about to collide with a Crane arm concealed in the clouds.
I was shoved up the river low level a few years back by Thames Radar and went as far as Tower Bridge before being turned back. This was because of IFR traffic.
One of the most amazing experiences looking straight down the chimney stacks of Parliament and into the busy streets below.
A Seneca twin flies very happily level on one engine.
If you did something totally stupid like running out of fuel it would not be that hard to put down in the Thames.
So I am a bit puzzled with the question too?
Pace