Or is it Nigel Mansell........The Stig seemed to know the Isle of Man road in that 3 car (Porsche/Aston/BMW) test rather well - and NM lives on the Isle of Man.

And his 1:44 in the reasonably priced car was also a coincidence. He took exactly the same driving lines as the Stig as JC commented!

There are other hints too but I cant remember!!