A cabinet minister has been accused of engaging in “gutter politics” after warning MPs that blocking Brexit could trigger a surge of far-right extremism.

Chris Grayling, the transport secretary, said that reversing the decision to leave the European Union would “open the door” to “extremist” populist political forces and lead to divisions not seen since the English Civil War.

Mr Grayling called on MPs to back Theresa May’s Brexit deal in a Commons showdown next week, as the prime minister braces for a historic defeat. Some estimates suggest she could lose by 200 votes.

His comments drew condemnation from Labour MP David Lammy, who described it as a “desperate attempt to use a tiny far-right minority to hold our democracy to ransom”.

Just days before the critical Brexit vote, Mr Grayling told the Daily Mail: “This is too important for political game-playing and I urge Conservative MPs who back Brexit and others to back the deal.

“If not, we risk a break with the British tradition of moderate, mainstream politics that goes back to the Restoration in 1660.”

He said there would be a “different tone” in British politics if Britain failed to leave the EU, and predicted a “less tolerant society” and a “more nationalistic nation”.

“It will open the door to extremist populist political forces in this country of the kind we see in other countries in Europe,” Mr Grayling said.

“If MPs who represent seats that voted 70 per cent to leave say, ‘Sorry guys, we’re still going to have freedom of movement’, they will turn against the political mainstream.”

Mr Lammy, who backs the Best for Britain campaign, said: “This is a desperate attempt by a government minister to use a tiny far-right minority to hold our democracy to ransom. It is gutter politics.

“History shows us appeasement only emboldens the far right and impoverishing the country through Brexit will only increase resentment.”

Ms Soubry, who was branded a "Nazi" by a mob who targeted her during live television interviews outside parliament on Monday, described Mr Grayling's comments as "irresponsible nonsense".

She tweeted: "The 15 yobs who have been roaming outside parliament do not represent anyone but themselves. It's shameful to validate them in this way.

"Right-wing extremists have always existed. Brexit is just an excuse - this is their real agenda."

Pro-EU MP Luciana Berger accused Mr Grayling of “cowering behind the small threat of far-right extremism” to avoid offering the public another referendum.

The Labour MP, who has been subjected to relentless abuse and death threats, said: “These remarks are not only grossly irresponsible but also show just how desperate supporters of this proposed withdrawal agreement have become.

“We absolutely need to heal divisions in our society but we will not do so with a Brexit that makes us poorer and offers less control.

“And the answer to a small band of far-right thugs roaming the streets must never be to capitulate and restrict our democratic engagement – it must be more democracy.”

Labour veteran Roy Hattersley dismissed the claims as “absurd”, adding: “I don’t think many people would regard Chris Grayling as an expert on these matters.”

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Lord Hattersley, a former Labour deputy leader who backs a Final Say referendum, told BBC Radio 4’s Today programme: “Nobody voted for Mrs May’s package. Nobody had the faintest idea what Mrs May’s package would be.

“It’s only reasonable that now we do know what it amounts to, what leaving really means, that people have an opportunity to vote on that. It’s a different vote.”

Lord Hattersley was due to address a People’s Vote rally in Sheffield on Saturday, along with Dame Margaret Beckett and Sir Vince Cable, but had to pull out due to illness.

The row over the transport secretary’s comments comes after a week of heightened tensions in Westminster, when Brexit secretary Stephen Barclay was condemned by MPs for saying the abuse hurled at MPs showed it would be too “divisive” to stage another public vote.