"the underground city at Burlington near Corsham (for use by our political masters whilst the rest of us dealt with the nuclear winter"
Site 3 (AKA Burlington / Turnstile / Stockwell) etc has not been a secret for nearly a decade. The more interesting question is what its role really was, as it seems that after 1963 it was primarily intended as a decoy site. (I'm a deep geek on Site 3, having been there several times and done a lot of research into it...)