I think I have cracked it. I am absolutely certain that the mystery car is the same as that labelled in my photograph " Balsa or is it". That photo even bears the outline of no.22 on its tail. The problem is that we have no photo of its front - until now. Attached is an albeit modern photo of what is undoubtably a Balsa, and I think this is Balsa-BMW no.2. Notice it is left hand drive, and has that perspex windscreen as opposed to the more common aero screen. It is quite different to the earlier Balsa - and note its cockpit shape. OK it has a different grille but I am 99% sure this is our car. I cannot of course explain why it is not driven by Marcel Balsa, who is on the programme as driving no.2O. I have peered at the film again and it is possible that he was driving the first Balsa-BMW, but I cannot be sure. On the version of the programme I worked on there were 3 "BMW Meteors" numbered 20, 22 Philippe and 24 Orley. I could not see one on the film, whereas I can make out the Duval and I think a Deho-Simca. I suspect the BMW Meteors were in fact all BMW specials.
Whatever, I think our car is a Balsa-BMW!