The last (official) RAF aircraft air-to-air 'kill' was an Egyptian Spitfire in 1948.
A number of RAF pilots have achieved kills whilst flying with other services, notably USAF in Korea and RN in the Falklands.
Allegedly, an RAF Javelin downed an Indonesian C-130 during the 1960s, and an RAF Hunter scored a manoeuvre kill against a MiG-17 at a similar time.
Though not an ace, there is still one serving RAF pilot who can claim to have destroyed a German aircraft (a Huey during an exchange tour, by crashing it). The Germans, with remarkable good humour, presented him with the stick-top mounted above a plaque saying "Confirmed Kill, Huey No XXX", plus date and his name!