I was told just after the Cold War that Boscombe Down was home to a couple of non-flyable MiGs and the odd Sukhoi. I suspect it was was probably true, since the information was relayed to me by a senior ETPS test pilot.
I seem to remmember, although I may be wrong, driving around the perimeter road having just had a AEF flight a few years ago and being certain that I had just seen a MiG-21 on the grass somewhere around the airfield. Pity you're not allowed cameras....