"Noticed on Jethros today that the next three new Q400s in the G-FLB sequence appear to be going to Olympic Air and have been allocated Greek registrations. Strangely they also seem to have been allocated UK registrations G-PTHA, B and C. If they are going to Olympic, why the UK registrations?"
I think it is becausa they are wet-leased; the aircraft would have to be flown by British crews. I guess the arrangement to lease was done with the approval of the aircraft's owners/lessors, who insisted on their being wet rather than dry leased.