Tory Neil Parish said he will resign as an MP after admitting to twice watching pornography in Parliament, saying he first accidentally viewed it after looking at tractors online before then acting deliberately.

The 65-year-old select committee chair, who is a farmer by trade, said the second time was while sitting waiting to vote on the side of the Commons chamber in a “moment of madness”.

He had been vowing to continue as the MP for Tiverton and Honiton after it was revealed he was the politician seen watching porn by two Conservative colleagues, but bowed to pressure to resign on Saturday.

The backbencher said in an interview with BBC South West that he recognised the “furore” and “damage” he was causing his family and his constituency in Devon before deciding “it just wasn’t worth carrying on”.

“The situation was, funnily enough it was tractors I was looking at, so I did get into another website with sort of a very similar name and I watched it for a bit, which I shouldn’t have done,” Mr Parish said.

“My crime, my most biggest crime, is that on another occasion I went in a second time, and that was deliberate.

“That was sitting waiting to vote on the side of the chamber.”

Mr Parish said it was a “moment of madness”, which he accepted was “totally wrong”, as he insisted he was “not making sure people could see it” and was trying to be discreet.

“I was wrong what I was doing, but this idea that I was there watching it, intimidating women, I mean I have 12 years in Parliament and probably got one of the best reputations ever – or did have.”

When pressed on why he chose to view the material in the Commons, he said: “I don’t know, I think I must’ve taken complete leave of my senses and my sensibilities and my sense of decency, everything.”

Deputy Labour leader Angela Rayner expressed bafflement at the MP’s excuse, adding: “Neil Parish must think you were all born yesterday. Boris Johnson’s Conservatives are a national embarrassment.”

The Tiverton and Honiton Conservative Association thanked Mr Parish for his “service to our communities” since becoming MP in 2010, adding: “We support his decision to step down as our Member of Parliament.”

The departure of the chairman of the Commons Environment, Food and Rural Affairs Committee will pave the way for a by-election in the Tory safe seat, which was won by Mr Parish by more than 14,000 votes over Labour in 2019.

Allegations of a porn-watching MP were first aired in a meeting with Chief Whip Chris Heaton-Harris on Tuesday.

Mr Parish did not come forward as the culprit, even when asked about the claims in a televised interview, until when the revelations were about to be made public on Friday.

The Conservatives then suspended the whip from him, meaning he was out of the parliamentary party.

He referred himself to the Parliamentary Commissioner for Standards Kathryn Stone, and said he would continue with his “duties” in the Commons pending the outcome of an investigation.

It was unclear whether that will still go ahead after he resigns.

But the Independent Complaints and Grievance Scheme (ICGS), which looks into claims of bullying and sexual harassment, can investigate former MPs.

It was understood the body had begun examining events after at least one witness made a referral.

A local Conservative source said the pressure to resign was coming from Westminster, rather than the constituency association.

Senior Tory Karen Bradley had urged Mr Parish to stay away from Parliament, while Harriet Harman, the longest-standing female MP, called for his immediate resignation.

But he insisted to reporters at his Somerset farmhouse on Friday that he would be carrying on while under investigation, suggesting that he had watched the porn accidentally.

However, it was hard to tally that explanation with suggestions that a Tory minister also witnessed him watching porn on a second occasion, in a committee meeting.

On Saturday morning, safeguarding minister Rachel Maclean said of his decision not to immediately stand down: “I genuinely think that’s a matter for him.”

But, speaking to Times Radio, she added: “I want to be clear, he is not continuing his business as normal, he’s under investigation, and I’m confident that the appropriate measures will be put in place to safeguard any of his constituents, particularly women and girls.”

Senior Conservative Caroline Nokes, who chairs the Women and Equalities Committee, accused the Tory whips of “dither and delay” over suspending Mr Parish.

Labour’s shadow Commons leader Thangam Debbonaire said Mr Parish was right to resign over his “disgusting behaviour”.

“But it’s shocking that the Conservatives have allowed this debacle to drag out over many days,” she added.

“Time and again the Tories refuse to act, resorting to cover ups and dragging the reputation of other MPs and the House down with them.”

Liberal Democrat activists relished the opportunity of a by-election, noting their success in taking rural seats off the Conservatives.

Daisy Cooper, the party’s deputy leader, demanded the Tories call the vote “swiftly”.