Before the current series of number plates came in 2001 a valid UK plate had to be 3 letters, a number between 1 & 999 and a letter.
So "THE 571G" is a perfectly valid plate, providing it is displayed with the correct spacing, and the numbers are clearly 571 and are not mutated to look more like STI.
I've never understood the appeal of so called vanity plates. There's a woman in Rochdale with the number plate "P380 OBS" with the spacing changed and the 8 changed into a B so the plate reads "P3 BOOBS"...
I once saw a very nice pink cadillac in Chicago with the number PRTYNPNK which was very apt. I tried to get one years ago when they were very cheap as it would spell my last name (legally) but I was told that BRA plates were not issued because of the connection to ladies underwear. Maybe things have changed now but the plate I needed was circa 1966. I also heard that someone from the West Midlands recently spent a few hundred thousand on an Edinburgh plate which is now on a LADA or something like that. Beggars belief.
Is it not more fun if you don't find out who he is!? It did seem as though he had been unmasked at one point. The Health and Safety Executive report into the Richard Hammond accident talks about an individual who "worked closely with Top Gear as a high performance driver and consultant", and then, of course, names him! The guy named has denied that it is him....If you google it you may come to the conclusion that there are in fact several Stigs.