It seems pretty clear that you can’t just move the fighter onto the sea zone, since the bid has nothing to do with changing the initial setup. The fighter could fly out and land during the US turn, if the carrier survives.
If you permitted it in this case, why wouldn’t you allow the UK to bid a carrier (with the BB and tran off Scotland) then just randomly move any two fighters onto it at the beginning of the game and change the entire setup thereby?
Just because you are only moving the fighter one square (from EUS to SZ) it still alters the setup dramatically.
and as other people pointed out, even if you protect this critical DD+2TT with the bid, they can still attack the UK one just north of it leaving UK with nothing at sea.