Sadly no proof, its one of those word of mouth things, but being a lover of top gear i have always wanted to know. So when my gf, got a job at NorthOne Television working as a researcher for fifth gear and the gadget show, I asked her to ask Tif who the stig was, so low and behold she found out, it made sense. Tif also said he was the Stig ages ago. Up to you guiys whether you want to believ it or not, the only way you would really find out is via this sort of method ie "inside info".
It doesn't stop there, one night about 9months ago I got a call from, Tiff (really cannot be arsed spelling his name my spelling and grammer is awful sorry) he asked me if I could swap roles with him for one evening? he wanted my gf for one evening and i got to be him for one evening which involved sleeping in the middle of nowhere in Whales for a shoot for 5thgear. Strange phone call but understandable as my gf was pretty hot and had half a brain, i told him no, he said "i can see why" but he seems like a really nice chap. Its a strange world i live in. I saw a thread linking to this forum where I am a long term member and honestly thought you guys may want some insider knowledge on stig, maybe i was mistaken.