R11 - The Human Centipede 2

From this, I learnt that some films break the regulations of the BBFC causing it to not be released in cinema due to the distress it can cause and for it's unfit audience. 
Even by watching the trailer i personally found it distressing and uncomfortable to watch as the main character relies on the main fears of the other characters to pleasure his own gains. 

However it wasn't the content of the film that got it banned, it was the basis of the film. 
The first Human Centipede film was based on a surgeon who kidnapped 3 victims and created a centipede amongst their bodies. The sequel is about a man who becomes sexually obsessed with the DVD of the original film.  In essence, the film is considered 'obscene' and 'absurd' which was thought to generate disgust amongst the audience. This is the reason why it was rated 18, as it focused too much on the sexual arousal and humility of the characters to be a 15 rated. However it was still released on DVD despite being banned from cinema's as it would put them in discomfort. I personally agree with the rating as even from the trailer, I think the content of the film is far too discomforting for anybody less than an adult to watch. Even for an adult to watch it, I find it very gruesome to think about who could even watch it.