It got me thinking were there other aircraft used,by the RAF that were one off’s.

As Graham says, lots! The RAF website even lists some of the impressed WW2 ones:

http://www.raf.mod.uk/history/CivilAircraftinWWIIService.cfm

and Foreign ones:

http://www.raf.mod.uk/history/ForeignMilitaryAircraftinWWIIService.cfm

Some, such as the Curtiss Condors, became instructional aircraft. Some lasted a few months (Fw200, Ford Trimotor) Others, such as the Boeing 247, had long and productive lives.

Pre-war, there were also a number of foreign types purchased for evaluation (usually by RAE or AAEE, but given RAF serials and markings (Breguet XIX, Heinkel He64, Dornier Komet, Dornier Delphin, Northrop 2E, Fokker FVII, Vought V66E, Junkers F13, Dewoitine D510 to name some of them)