Jake Davison, the gunman behind a mass shooting in Plymouth that left six people dead including the perpetrator, posted numerous videos on YouTube just weeks before the massacre.

The 22-year-old appeared to be active on several online platforms and his accounts suggest an interest in the so-called “incel” movement.

Despite mentioning it and following a YouTube page called Incel TV, Davison said in one of his videos that he “wouldn’t clarify myself as an incel”.

Here, we look at what an incel is, how the movement started and what is being done to address it.

– What is an incel?

The incel subculture of self-professed involuntary celibates is a “deeply sexist and misogynistic” development of age-old sexism that has been boosted by the rise of internet communities, according to a University of St Andrews expert.

“This isn’t sophisticated but the problem is the volume of people who might be flirting with this kind of scene,” said Tim Wilson, director of the Centre for the Study of Terrorism and Political Violence at the University of St Andrews.

“There’s been plenty of sexist, violent men since the dawn of history but the sense of this being a public movement could not exist without the rise of social media and the internet.

“The basic idea, I’m afraid, is the idea that sexual fulfilment is a human right and that as a man not getting it, you’re somehow being actively deprived and repressed by women.”

Antifascism campaign group Hope not Hate said it is too soon to say what motivated the attack, but warned that the incel ideology can be “dangerous and radicalising”.

“It is built on misogyny and a twisted, desperate world view,” a spokesperson said.

“We do not know what motivated this horrendous incident, however those who consume incel content have engaged in violent attacks.

“Whatever happened in Plymouth, the hatred of women – and the communities of men who engage in a celebration of that hatred online – must be taken seriously, in schools, by social media firms and by Government.”

– How did the subculture begin?

The incel movement gained momentum in 2014 after the Isla Vista killings by Elliot Rodger in California.

He murdered six people before turning his weapon on himself in an act of violence he described as his “war on women” who were not attracted to him.

The killer posted videos of himself online setting out his “manifesto”, as well as declaring he would get revenge on women and sexually active men.

Mr Wilson believes Rodger was a turning point for the subculture as it made him into a “hero” – with some calling him Saint Elliot.

He said: “We have these very dark corners of the internet where lonely, frustrated people can be attracted and reinforce each others’ prejudices and world views.

“Out of that comes a grey borderland of socially disturbed killings.”

Just last month in the US, Tres Genco, a 21-year-old from Ohio who described himself as an “incel” in YouTube videos, was charged with plotting a mass shooting targeting women in university sororities.

– How can it be tackled?

Mr Wilson said incels should be treated as a “quasi-political” movement for it to be tackled by authorities.

Last month, Caroline Dinenage, minister for digital and culture, was asked by Labour MP Bell Ribeiro-Addy whether the Government’s Online Harms Bill will address rising concern about incels.

“The Online Harms Bill will make much clearer the links between what online companies say they do and what they actually do, and women will be better supported to report abuse and should expect to receive appropriate, swift action from the platform,” Ms Dinenage said.

“In addition, we have sponsored the Law Commission review on harmful online communications, looking at whether the law needs to be tightened around this issue.”