Peeping Tom is a nickname commonly given to voyeurs, particularly males. It originated with the legend of Lady Godiva, when a man named Tom watched her during her nude ride and was struck blind or dead.
The film was heavily cut by the BBFC before release and consequently many scenes still have a ragged feel to them. The murders of Vivian and Dora were toned down, shots of nudity were deleted (including photos of nude girls in the album), the suicide of the killer was shortened, and scenes featuring the spike were also edited. Some dialogue was also cut (which explains the abrupt ending to the conversation between the policemen in the car). Although some cuts were restored in later video and DVD releases much of the edited footage is now considered lost forever.
The above were some stuff I found online.
I thought the movie was overal pretty good, Mark was freaky, but it kind of dragged at parts. I found a lot of interesting and funny goofs and other facts on IMDb about the movie. It was certainly ahead of it's time.