Image copyright Getty Images Image caption Campaigners say that victims often have feelings of guilt

Lisa is one of a number of young women who have told the BBC they have been pressured into acts of violence in the bedroom.

She says she willingly "got together" with a guy she "kind of knew" at a house party but was shocked when he began repeatedly biting down on her body.

"When he pulled his mouth away, his teeth were still clenched. I thought he was going to tear chunks out of my skin," she says.

Lisa, which is not her real name, said there was no conversation beforehand about whether she wanted to be bitten and she was physically shocked by it.

She says she was crying and asked him to stop "but there's only so much you can do when somebody is a lot larger and stronger than you are".

Online culture is changing behaviour in the bedroom and what was once regarded as strictly fetish is rapidly becoming the norm.

BBC Disclosure and BBC 5Live commissioned a survey of 2,049 UK men aged 18 to 39 to assess how so-called "rough sex" was being navigated.

In the survey, 71% of the men who took part said they had slapped, choked, gagged or spat on their partner during consensual sex.

One-third (33%) of the men who had done this said they would not ask verbally whether their partner would like them to do it either before or during sexual activity.

Which of the following have you performed during consensual sexual activity? British men aged 18-39

What is driving this interest in so-called "rough sex"? Our survey of young men pointed to a big factor - pornography.

More than half of the men (57%) who had said they had slapped, choked, gagged and spat on partners said pornography had influenced their desire to do so.

One in five (20%) said it had influenced them a "great deal".

A man called George - not his real name - told the BBC Disclosure programme A Question of Consent that he had tried choking and slapping during sex.

"You see it in porn and think, 'oh, that looks class' and you try it," he says.

However, George says it can be disappointing when re-enacting what you watch on free pornography sites.

"It never turns out the way it looks in porn," he says. "Obviously, they are actors, even though you watch and you like it, when you try it in real life you are disappointed quite a lot."

To what extent do you think pornography influenced you? All respondents who "have performed" slapping, choking, gagging or spitting

Dr Fiona Vera-Gray, from Durham University, researches the clips, titles and thumbnails found on the front pages of the world's most popular free pornography sites.

She says she found evidence on the first page of the sites of all kinds of videos that would not be allowed to be uploaded under their stated terms and conditions.

Dr Vera-Gray says she even found evidence of videos that "promote, endorse or glorify sexual violence, such as rape".

She says: "Porn has changed the landscape of what's going on for kids and so if you think your 12-year-old hasn't seen pornography, I'd really question that."

BBC Disclosure approached the most popular free pornography sites for an interview. None agreed.

Lisa, who is in her 20s, told the programme how she felt after her encounter.

"I was just in shock," she says.

She says she felt a bit guilty because she had "gotten with him".

"Could I have done more? Could I have said more? Could I have left?" she says.

She asks herself: "Did you do enough to stop it?"

Image caption Brenna Jessie said women were often made to feel guilty

Brenna Jessie, from Rape Crisis Scotland, says that feelings of guilt are really common among victims of abuse.

"I think there will be a lot of women who have consented to sex but who have not consented to violence who won't necessarily recognise their experience or understand their experience to be sexual violence," she says.

Ms Jessie believes that society is to blame for those feelings.

"We live in a society that really shames victims and blames them for not doing more to keep themselves safe rather than asking the perpetrators - or the people, who have committed these acts - why they have done that?"

Disclosure: A Question of Consent is on BBC1 Scotland at 22:45 on Monday 23 March and on the iPlayer.

Previous Disclosure investigations include: