Well you only have to look at all the GA airports in and surrounding London to see see that the "BizJet World" has been hitting a peak for a while now.
Lots of positive stuff happening at most FBO's with some form of expansion or upgrade of service. I would steer clear of working for an airline well a small one anyway,as with the loss of so many in recent months we will no doubt see a few more casualties yet!
As for what companies are about, Signature LTN,Harrods LTN & STN ,Tag FAB, Inflite STN, Universal STN not forgetting London City Jet Centre, Biggin Hill do a search and you find them all on here.
Good Luck