That's it - since I'm moving to Hastings but need to be in London a couple of times a week I'm buying a Lake LA4-200 Renegade. Tie her to the pier in Hastings and then tie her to HMS Belfast's anchor chain when I'm in London..
Thruth is, the Thames isn't very heavily trafficked anymore. It could easily accomodate some seaplane movement to the East. It's also insanely wide there, so there's plenty of room.