The RN FAA and the AAC have some weekend reserve (not FTRS) aircrew. In all cases they are former regular/full time service aircrew.
7 Rgt AAC (V) info
"The criteria for pilots to join are that they must have completed the Army Pilots’ Course, and previously served in the regular Army (even ex-Royal Navy pilots who were attached to Army units have served in the Regiment and we do have a number of ex Royal Marine aircrew). Most pilots serve between 40 – 60 days a year, the majority of that as single pilot operations."