The new Independent Group of MPs has agreed to back Theresa May in any vote of no confidence, one of its most prominent members has said.

In an exclusive interview with The Independent, former Conservative MP Heidi Allen said the group – which also consists of eight Labour MPs – had decided not to do anything that would facilitate a general election.

Her words go further than previous comments that the group might support Ms May in a confidence and supply arrangement if she agrees to soften her Brexit stance.

The ex-Tory MP also pledged that the new group would do things more professionally, revealing she had been staggered arriving in Westminster to find ministers were not experts in their briefs and MPs had to be given “paper with helpful things to say”.

It comes after Ms Allen, and her previously Conservative colleagues Anna Soubry and Sarah Wollaston, savaged their former party, claiming it had fallen into the grip of the eurosceptic European Research Group. Ms Allen even suggested the new group would lead to the destruction of her old party.

Asked what the Independent Group would do in the instance of a no confidence-vote brought by the opposition in Ms May’s government, Ms Allen said: “This is all such a jigsaw, it is very hard to game plan.

“But what we have definitely agreed is that anything that would facilitate a general election we wouldn’t support.

“To the contrary, we are hoping that us three Tory, or rather ex-Tory women, will have been a wake-up call to the prime minister.”

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Another member of the group, ex-Labour MP Gavin Shuker, has previously suggested that the new group could replace the Brexit-backing DUP as the government’s confidence and supply partners, but only in return for a softer Brexit.

Meanwhile, all of the MPs have indicated that they will not hold by-elections in their seats despite pressure to do so, having been elected as members of their previous parties.

Ms Allen said she found it “utterly staggering” coming from a world outside politics to discover how the party system worked.

She said: “I was not involved in politics at all. I didn’t watch Question Time. It was literally a standing start from nowhere in 2012.

“I contacted my local association. I went on Google. I didn’t even know how you do it. I assumed from the outside that everything would be, you know, a big team, the sharpest minds, the best people in the business. The health secretary, or the defence minister or whoever it might be would of course be the expert in that field.

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“And I was just shocked when I got there about how it’s really not like that. And it’s ooh, guess what, they give you bits of paper with helpful things to say written on them. I found that utterly staggering.”

She vowed that any party formed from the Independent Group would do things differently, without the “aggression” of other parties.

She added: “I want it to be based on evidence and analysis, expert opinion. MPs having a training and development plan.

“You know, ‘You used to be in the army, over time would you like to be a minister? You’ll need to put some time into your personal development.’ A sense of team.”

Earlier on Friday, Ms Allen said it was “obvious for all to see” that Chuka Umunna was the clear candidate for a leader of any new party formed from the group and he was most capable of getting “the best out” the MPs.