The biggest shake-up of British politics for a generation appears set to continue after three MPs quit the Conservatives and encouraged others to follow them to the new Independent Group.

Heidi Allen, Anna Soubry and Sarah Wollaston hit out at Prime Minister Theresa May’s “disastrous” handling of Brexit as they resigned from her party.

Ms Allen made clear that she wanted the new centre-ground group, which already contained eight ex-Labour MPs, to become a party that would eventually eclipse the Conservatives.

She claimed ministers “at all levels” in Government were sympathetic to their decision to cross the floor in the Commons.

They made clear that their concerns about Mrs May’s performance went far wider than Brexit, accusing the PM of throwing away the modernisation agenda begun by David Cameron and allowing the party to be taken over by right-wing hardliners.

Ms Soubry said she would not stay in the Conservatives to “skirmish on the margins when the truth is the battle is over and the other side has won”.

She said: “The right wing, the hardline anti-EU awkward squad that have destroyed every leader for the last 40 years are now running the Conservative Party from top to toe. They are the Conservative Party.”

The Broxtowe MP urged “fellow one nation Conservatives” and “like-minded Lib Dems” to “please, come and join us” by breaking away from their parties and joining the new grouping.

The three blamed “Blukip” or a “purple Momentum” of hard-right “zealots” for trying to force out MPs on the Remain wing of the party through deselections.

They claimed Mrs May had shown a “dismal failure” to stand up to the European Research Group of Brexiteer Conservatives, who were operating as a “party within a party” at Westminster.

Former minister Ms Soubry, Totnes MP Dr Wollaston and South Cambridgeshire MP Ms Allen – who dubbed the group the “three amigos” – said they could “no longer act as bystanders” as Mrs May continued with her Brexit strategy.

Ms Allen said she believed “a significant number” of Conservative MPs were considering joining the new group.

Asked if she could ever envisage returning to the Tory fold, Ms Allen made clear her ambitions for her new movement: “If we do our jobs right, there won’t be a Tory party to go back to.”

Although the group has yet to formally become a new party and lacks the organisational infrastructure necessary to fight elections yet, Ms Allen predicted it would be a force to be reckoned with at the next general election, telling the BBC: “I think I would be disappointed if we weren’t pushing for second place at least.”

A YouGov poll suggested 14% of voters would back the breakaway group if it stood candidates, with the Tories on 38% and Labour on 26%.

(PA Graphics)

The move brings the tally of TIG MPs to 11 – equal to the Liberal Democrats and one more than the Democratic Unionist Party, who prop up Mrs May’s minority administration in the House of Commons.

Lib Dem leader Sir Vince Cable offered to work with the new group, hinting at a possible electoral pact by saying it would be “foolish” for them to stand candidates against each other.

Chris Leslie, one of the original seven who quit Labour to form the group, said although they would be willing to co-operate with MPs from all parties “we are not joining the Liberal Democrats”.

Independent Group MPs
The 11 MPs who make up the new Independent Group at Westminster (Stefan Rousseau/PA)

As well as Brexit, Ms Allen, a member of the Work and Pensions Select Committee, made clear she was also opposed to the Government’s stance on welfare.

“I can no longer represent a Government and a party who can’t open their eyes to the suffering endured by the most vulnerable in society, suffering which we have deepened whilst having the power to fix,” she said.

Dr Wollaston, who chairs the Commons Health Committee, said: “I am afraid the Prime Minister simply hasn’t delivered on the pledge she made on the steps of Downing Street to tackle the burning injustices in our society.

Independent Group of MPs
(PA Graphics)

“I think that what we now see is the party, that was once the most trusted on the economy and business, is now marching us to the cliff-edge of a no-deal Brexit.”

Mrs May said she was “saddened” by the decision but insisted that “we are doing the right thing for our country” by delivering Brexit.

She added: “I am determined that under my leadership the Conservative Party will always offer the decent, moderate and patriotic politics that the people of this country deserve.”

A Downing Street spokesman said the three MPs’ Conservative associations were now free to select new general election candidates but said he was not aware of any central directive to do so.