The number of participants was somewhat lower than the 1,100 who had said they were planning to attend, but what the demonstration lacked in protesters it made up for in onlookers and gawpers wielding camera phones.
The catchy slogans on the protesters’ banners included “Urine for a shock if you expect us to stop” and “We fought to be seen, do not ban us from the screen.”
They accompanied their face-sitting, appropriately, with a rendition of the Monty Python song Sit On My Face and chanted: “What do we want? Face-sitting! When do we want it? Now!”
Many said they were upset about censorship and the fact that the new law was announced “without any discussion.”
“They’ve done this without public knowledge and without public consent.
“There are activities on that list that may be deemed sexist, but it’s not just about sexism, it’s about censorship. What the Government is doing is taking our personal liberties away without our permissions.”
Ms Rose issued a handy checklist before the protest, warning people to bring a coat and a mat to lie on, as the inclement weather threatened to make it a chilly affair.
She also wrote on Facebook: “Remember to keep hydrated, face to sit on? And some smiles? See you all later today beautiful people.”
Among the unusual scenes witnessed was a man wearing a snorkel and a demonstrator being whipped – all in the name of free speech.
Around 22 couples took part in the actual face-sitting part of the protest.
But there was some confusion among the onlookers as to whether it was legal for them to photograph the stunt, and if so, would they be arrested for publishing the pictures?
Scotland Yard said it would be monitoring the protest but refused to say whether anyone simulating sex acts in public would be arrested.
A spokesman would not be drawn on the legality or otherwise of the protesters’ activities.
A Metropolitan Police spokesman said: “We are aware of the protest due to take place between 12pm and 3pm.
“We have been in contact with the organiser. The event is being stewarded.”
There was no obvious police presence as the demonstration got under way, however.
Adjudicators were on hand to ensure no-one was in distress, armed with facial colour charts for health and safety showing that pink is healthy and blue means suffocation.
Jane Fae, co-convener of the Calm Consenting Adult Action Network, said: “It seems to be no surprise that the Government is putting in place regulations that help the big porn businesses.
“People have been doing the respectable thing for years and years. But the Government has its own agenda and if this shines a light on what the Government’s doing then it’s a good thing.”
The Liberal Democrat MP Julian Huppert is also campaigning for the new rules to be reviewed but was not in attendance.
Obscenity lawyer Myles Jackman, Jerry Barnett from Sex and Censorship and Jane Fae from the Consenting Adult Action Network were among those making speeches at the protest.
Ms Fae called the changes “heteronormative”, and said: “What is being clamped down on is any kind of online content made by adults who are consenting.
“This is entrenching big business.”
The change in legislation, which came into effect this month, means 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 Classification, are prohibited.
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”.
Mistress Absolute, 39, a professional dominatrix and fetish promoter who attended, said the law was restrictive.
“I felt that this was the beginning of something to creep into my sexual freedom and sexual preferences,” she said.
“This is a gateway to other laws being snuck in.”
Her friend Neil Rushton, 33, a mature student, said: “They’re very sexist laws. These are very geared towards women’s enjoyment as opposed to men’s.”
Justin Hancock, a sex educator who runs the website Bish UK, said: “Often the same filters that block these websites block my website, so I suffer from the same kind of censorship issues that the porn industry does.
“This particular regulation will not prevent one person from seeing any porn that they can’t already see elsewhere anyway.
“Them using the argument around sex and young people is completely specious.
“It’s moralising. It’s about saying as a society what kind of sex is okay.”
Mr Hancock also warned that the “state is trying to take control of the internet”.