Well, I guess, if even Kostas is not on the spot, then this was unexpectedly hard one. That's FV-4030 Shir-2 and yes, it was a prototype also to Challenger Mk.1. So I guess Golly has to decide who was closest.
well I call it unsolved, and you may post a new pic...only correct answers count, not close ones (untill they are practically sharing the same bedroom )