A list of sex acts has been banned from online UK porn videos in a bid to crack down on "harmful" content.
A quiet change in UK legislation has ruled that paid-for online porn videos must now adhere to the same rules as content produced for sex shop-type videos.
It means acts that would not be classified as an R18 rating, in line with guidelines laid out by the British Board of Film Censors (BBFC), are prohibited.
The list of around 10 acts reportedly range from spanking to strangulation.
Critics argue the change not only damages the country's porn industry, with online viewers still able to access content banned in the UK by watching videos filmed abroad, but amounts to "arbitrary censorship".
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"R18 is a strange thing," Jerry Barnett, founder of anti-censorship campaign Sex And Censorship, told Vice News.
"It's a set of weird and arbitrary censorship rules decided between the BBFC, the police and the CPS (Crown Prosecution Service).
"There appear to be no rational explanations for most of the R18 rules; they're simply a set of moral judgments designed by people who have struggled endlessly to stop the British people from watching pornography."
The Audiovisual Media Services Regulation 2014 came in to effect on Monday.
A spokesman for the Department of Culture, Media and Sport said the new law gave the the online world equal protection.
"In a converging media world these provisions must be coherent and the BBFC classification regime is a tried-and-tested system of what content is regarded as harmful for minors."
Erotic film director Erika Lust criticised the new legislation for cutting back on acts associated with women's pleasure and said women in the industry will now fear the loss of their livelihoods as well as their sexual independence.
