Confirmed by a worker that Gulfsteam will retain just a man in a van at Luton when they move to Farnborough. There was a rumour that they would retain some sort of mini base at Luton.
The issue for Signature is that its passengers are governed by the same restrictions as everyone else. There was a story circulating at Signature that while the American crew of a biz jet could fly Luton to the good old USA the British owner of the jet could not.