I think BRG should be good enough
But you're absolutely right, anyone who is serious will hop on a plane and eyeball it. I've bought cars from GB, some a lesser prices than this, I flew over, and sometimes walked away again, and other times drove home, even from Southampton to Stranraer to the amazement of the previous owner.
Those of us on the perifery of the U.K. do that, those in the centre seem more reticent to do so.
If you're going to buy a car above £10k, surely a 100 quid flight is a worthwhile investment?