FCL do accept Bulldog and Grob hours and have always done so for PPL currency. What they do not do at the moment is accept a military flight test to be accepted in place of a civilian flight test to automatically renew the PPL if sufficient hours have not been completed. However, if you have a lesson with a UAS intructor who is also a CAA instructor, then that does count as the hour of instruction required among the 12 hours in the second twelve months of PPL validity.
This all stems from as is rightly said that they are Single Engine Piston hours, as would hours from flying in another country also count.