Apparently, the Board has recommended that one examiner on his own views the films, instead of two, in order to cut costs. Well, they don't like this.
According to The Register
The "examiners", however, say that "films that are refused an R18 certificate often include scenes that many find disturbing, including sadomasochism and sexual violence", adding that "viewing pornographic content alone will increase the chances of being sexually aroused by the material".
Well, bugger me. I knew there were side effects associated with viewing porn (so I am told) but sexual arousal did not occur to me.