Not quite as long as Shuttleworth's DH-60, but Monsun G-AYPE has been at Biggin since it was imported by Air Touring Services in '71 and with the same flying group since '74 - nice to see it a few days ago, it is very active!
(Grasshopper G-BBLH has been there since certainly '77 - I saw it there in very early January '77 looking very nice in its USAAC scheme - and looking at the previous owners, possibly as early as '74)
Speaking of Shuttleworth and Bristol Bulldogs, they of course had one that was spectacularly demolished at Farnborough in '64 after and engine failure at the top of a loop. The pilot escaped with cuts and bruises. Eventually painstakingly rebuilt by Skysport, it's now on display at Hendon.