If I had something with a bit of pace e.g P51,TBM 850 etc I would have a go at the Humber bridge-plenty of room between water and road level.
Transponder on but no height info dive from 1000' and pop back up at 300kts ish! to fast for anyone to get the reg if you did it early on I reckon you would get away with it.(you could bribe the radar controller not to say anything with some beer!)
