Tourist - yes, I'm sure I've heard that somewhere....it may have been along the lines of 'no ejection unless/until you are sure your a/craft is going in the drink'.
It would be kinda poor form for a military pilot to bang out over central London and let his a/craft do it's own thing. I think the routes to get to the Mall take into account water and open areas as much as possible.
Anyway, there must be some on here who can confirm or otherwise.