Sex workers and campaigners have gathered in front of parliament to protest against changes to UK pornography regulations.

Organiser Charlotte Rose called the restrictions “ludicrous” and said they were a threat to freedom of expression.

Protesters say the list of banned activities includes “face-sitting”, and campaigners planned to carry out a mass demonstration of this while singing the Monty Python song Sit On My Face.

“These activities were added to this list without the public being made aware,” Charlotte Rose said. “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.”

Protesters outside parliament. Photograph: Andy Rain/EPA

The protest comes after the government said a list of sex acts has been banned from online porn videos filmed in the UK, in a bid to crack down on “harmful” content.

A quiet change in 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 Classification (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”.

The Audiovisual Media Services Regulation 2014 came into effect this month.

Mistress Absolute, 39, a professional dominatrix and fetish promoter, said the law was restrictive.

“I felt that this was the beginning of something to creep into my sexual freedom and sexual preferences.

“This is a gateway to other laws being snuck in.”

Protesters outside parliament. Photograph: Vianney Le Caer/Rex Features

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.”

The pair will take part in the mass face-sitting this afternoon.

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.”

Hancock also warned that the “state is trying to take control of the internet”.

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.

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.”

Protesters chanted: “What do we want? Face-sitting! When do we want it? Now!”

Participants wearing gimp masks used mats and blankets to act out face-sitting.