Just be aware that traditionally LGW - LHR moves have been "subject to the needs of the service BA". People who have had valid, accepted bids onto LHR fleets have had them delayed and even cancelled as their position at Gatwick couldn't be "backfilled". I believe the same is true of EF, although I haven't checked the scheduling agreement so can't say for certain.
I'd check that contract carefully if I were you. Traditionally Gatwick was the hidden gem at BA, probably because it was practically ignored by waterside - a double edged sword as we saw in 2020.