Hi,
The only thing I can suggest is doing a search on the CAA G-INFO database for aircraft types like Navajao, Seneca and Seminole etc and seeing where some of them are based.
Otherwise, for a Seneca you can try Truman Aviation at Nottingham, £209/hr wet. I'm led to beleive that a setup based at Gamston also has a Seneca...can anyone confirm this?
Cheers
Obk