John, there's bound to be one around somewhere not too far away. I know the feeling, after about 35 years I spent a lot of time learning all about the Centurion again, and the day I lifted engine and transmission decks after all those years was quite a moment. (Sad isn't it?). I didn't actually lift them on my own, as I did whilst a driver, but it was good to see all the gubbins again. I drove one as well, gear changes not quite as slick I fear. Probably best not to go down the "corporate tank driving " avenue, you might be disappointed. Not to mention empty of wallet.
I googled "Chieftain tanks in the North of England" and a few things came up, but all appeared to be business things. Someone will know I'm sure. I'll ask the question on our old comrades web forum, but will probably get a load of "humourous" replies!