Historical question
 

When was the last time an RAF aircraft shot an enemy aircraft down?

1945

Several RAF Harrier pilots shot enemy a/c down during the Falklands war in '82, but all flying RN Sea Harriers whilst on exchange.

If you count forcing the other aircraft to manoeuvre in such away that it crashes (allowable for ace calculations) it was September 1964, Indonesian Confrontation when a 60 Sqn Javelin chased an Indonesian C-130B which vanished from radar and was presumed to have flown into the sea. The aircraft was later confirmed missing from base by Canberra recce missions.