My count is four - once I was working at a company in Bicester in the early 90s (when Upper Heyford was still operational) I happened to step outside to witness an F-111 in its final throes of crashing, trailing a great tongue of flame (the crew attempted to dump fuel before they left with the cockpit). The a/c came down in a factory car park just outside the town. Fortunately there were no injuries although I recall one bloke had a lucky escape - typical story of 'the plane just kept getting bigger' before he dove under a parked car.
Three display crashes - Yak-18 at White Waltham (no injuries), Sea Fury at Prestwick (gear stuck - pilot bailed out over the Clyde), and the Spirit of St Louis replica at Coventry (my only fatality). Oh, I suppose the G222 scrape at RIAT a few years back also counts.