AD Aviation operate a Citiation 501SP and two C550's at Liverpool. There is also Ocean Sky at Manchester with two CL604's and NEA I think still have an AOC with Lears. Nothing at Blackpool nowadays, all have stopped operations. There is a C550 at Hawarden too. Mannair sold the Navajo and Chieftain to Synergy at Fairoaks. I think Ravenair are the only piston twin operaters this way at the moment.