Six years ago, a poster on the Cult Movie Forums forum (then the forum for Anchor Bay UK) alleged that his UK "pre-cert" VHS was the '71 original version, and that the BBFC listing of 95 minutes seemed to be correct. He still posts on the board even now, so may be able to help.
http://www.cultmovieforums.com/forum/showthread.php?t=3525&highlight=thx+1138