"I’ve never done this before with my trousers on!"

A comment from one of the participants in the UK’s first ever face-sitting protest sets the tone for the afternoon. It’s a first for all involved, with 21 pairs of face-sitters and face-sittees gathered outside the Houses of Parliament to protest against the introduction of new porn censorship laws.

Activities like female ejaculation, spanking, caning, fisting, and — yes — face-sitting are all being subjected to new restrictions, with regulator ATVOD (the Authority for Television on Demand) calling for strict guidelines that bring the laws for adult video-on-demand sites in line with those for R18 DVDs sold in licensed sex shops. ATVOD says it's merely ironing out "a regulatory inconsistency," but the protesters say it’s censorship.

"Can anyone define ‘aggressive whipping’? If I'm whipping you with a smile on my face, do I look aggressive?"

"The government claims that this law is needed to ensure consistency, but who do they think they are in taking our rights away to view legal and consensual sex online?" says Charlotte Rose, the protest’s organizer, a sexual rights campaigner, and Sex Worker of the Year 2013. "Can anyone define ‘aggressive whipping’? If I'm whipping you with a smile on my face, do I look aggressive?"

For regulators and protestors alike, the devil’s in the details. Myles Jackman, a lawyer specializing in obscenity and pornography who supports the protest, points out that it's a bureaucratic nightmare. For example, under the new regulations, porn involving "purpose-designed fucking-machines" is acceptable, the use of standard power tools is not "since most people have one lying around at home."

Similar caveats are being applied to fisting (okay ‘up to the last knuckle’) and female ejaculation ("acceptable if not performed onto another person and/or then consumed"), with regulators saying they’re only worried about porn consumers copying these acts and hurting themselves. Pete Johnson, chief executive of ATVOD, says that he blames "grossly inaccurate accounts" of the new law for the outrage, with some articles from the UK media falsely describing the acts affected as being "outlawed outright."

"There is no ban on face sitting," Johnson tells The Verge. "What there is, is a concern on a deliberate focus on the restriction of blood or oxygen to the brain because its potentially fatal." He’s also keen to stress that there’s no gender bias or "bias against activities associated with particular sexual preferences." However, this is a difficult line to take, especially when comparing the restrictions placed on the depiction of female ejaculation and the freedom concerning male ejaculation (consuming this ejaculate is okay). ATVOD says it's because it can’t draw the line between female ejaculation and urination, but the protestors say it's an attack on female sexual agency regardless.

Regulators say porn can't look dangerous - protesters say that's what makes it porn

Although the popular line taken by some protesters — that politicians are trying to make everyone as sexually repressed as they are — is unconvincing, many participating in the mass face-sitting note that the appearance of danger is sometimes integral to this type of pornography. "I think that part of the point of that type of image is that it has to look like someone’s maybe in peril and is being dominated," says Sebastian Bird, a software developer and self-described submissive who came out to protest. "One of the reasons given [for the law] is to protect children or young people from porn, but they’re not actually targeting the free sources of porn these children are all watching: the tube sites."

For protest organizer Rose, though, even partial restrictions are censorship enough. "This is absolutely ludicrous that this was done secretly behind closed doors without the public being aware," she shouts from the steps of a historic monument, surrounded by a huge press scrum. "Did I consent to this? Did you consent to this? This affects our sexual freedom. The freedom to express yourself in the things we enjoy and consent to."

After the speeches, Rose corrals the crowd, lining up participants and making sure there are yoga mats and blankets for all on the cold paving stones. Everyone is laughing and smiling as they pair up, some posing for the cameras and others for selfies. An onlooker shouts "For the love of God, someone sit on that poor fella's face!" as the last couples arrange themselves. Finally, the hymn sheets are handed out and a rousing rendition of Monty Python's "Sit on my Face" begins. Some of the voices are a little muffled — but at least they're being heard.