Censorship of films has always been a thorny issue, where the censors will never be able to please all in their decisions.
The British Board of Film Censors (BBFC) was founded in 1912 as board independent of the government and the film makers. .
They had two classifications of film at this time. These were "U" for films suitable for all and "A" for adult audiences only. .
The BBFC was made responsible for all cinema just a year later, up until this point it had been up to local councils to make the decision, so what could be seen in Bristol or London, may not be seen in Manchester for example. The local councils could still overrule the decisions of the BBFC, from the 1920s they generally accepted the decisions of the Board.
In the early days, the Board had, under President T. P O"Connor, drawn up a list of 43 "Grounds for Deletion." This was a list which was used by the BBFC's examiners as reasons to censor films, and were very representative of their the time. Whereas scenes of drug addiction ("Trainspotting" (1996)), realistic horrors of warfare ("Apocalypse Now" (1979)) and men and women in bed together (just about any film or television programme) are more acceptable now, and looking back seem draconian but were reflective of those days.
As times changed, so did the attitudes of the Board on what could and couldn't be screened on general release. The 1960s saw the Board start to go with the liberal attitudes of the time, and scenes of sex, drug taking and violence became more acceptable.
The 1980s saw the Board change it's name from Censors to the British Board of Film Classification, and also the renaming of the classifications from the old A and X's to the age classifications we have today.
1984 also saw the Government bring in the Video Recording Act. Up until this point, the sale of video cassettes had been unregulated, and the "video nasties", "Driller Killer" et al, were sold uncensored and unclassified.