If I remember correctly Air Foyle were going to use the Jetstream for charter work. They did do a few proving/training flights, because a few of us from ATC went along for the ride. One was in Aug 1994, and went Luton - Bristol - Exeter - Southampton - Luton. The second one we went on was in Nov 1994 and went Luton - Bournemouth - Luton - Leeds - Luton. I can't remember which one it was but on one of the flights the Captain was an ex BA Concorde captain being trained on the Jetstream. I don't think the proposed work got off the ground though. (Excuse the pun)
As far as GBKUY being used by McAlpine, it was also used for charter work, and was used once on the Mail on Sunday run to Manchester in October 1985, which I was fortunate to be on!