Cabinet ministers including Leave-backers like David Davis and Boris Johnson want Theresa May to loosen some of her Brexit "red lines" because they have "hamstrung" negotiations, a former senior government adviser has suggested.
James Chapman, who was Brexit Secretary Mr Davis's chief of staff until the snap election, said the Prime Minister's "absolutist" positions have made life very difficult for his former boss as he conducts talks with the European Union.
He suggested Mrs May should loosen her commitment to leaving the jurisdiction of the European Court of Justice (ECJ) and hinted that Mr Davis and Mr Johnson could back a more liberal approach on immigration.
And he said the PM must reconsider her decision to withdraw from the European Atomic Energy Community (Euratom), which governs the peaceful use of nuclear energy within the EU, or MPs would overturn it for her.
Mr Chapman's revelations came in an interview with Times deputy political editor Sam Coates for BBC Radio 4's The Week In Westminster.
The former adviser said of Mrs May: "Where she's taken some absolutist positions on particular issues, I'm thinking of the European Court of Justice.
"She's set a red line effectively for a conference speech that hamstrung these negotiations in my view."
On Mr Davis, he went on: "There isn't anyone better to do this negotiation in Parliament in my view.
"He's a very tough, resilient operator. There have been red lines that have been set for him, that make the job he has to do very difficult."
Asked by Mr Coates if Brexit-backers in the Cabinet would want the PM "to loosen some of the absolutes that she set before the election", Mr Chapman replied: "Well, if you consider the two most powerful Brexiters in the Cabinet; David Davis and Boris Johnson, they're actually pretty liberal on issues like immigration.
"I think that there would be room to recalibrate some of this approach but at the moment she is showing no willingness to do this, I mean she said that when she delivered the Lancaster House speech that's the plan and that's what she is sticking to.
"Now this is a new Parliament, there's a new reality. She has to get these things through Parliament. There's an enormous amount of legislation. All sorts of moments where she's going to have to carry the Commons, let alone the House of Lords with her.
"So if she doesn't in my view show more flexibility, show more of the pragmatism that she did demonstrate in the Home Office, she won't get this stuff through Parliament."
Mr Chapman said Mrs May has apparently committed to leave Euratom because "there's a locus" for the ECJ in the treaty which covers the free movement of nuclear scientists.
"Now I would have thought the UK would like to continue welcoming nuclear scientists who are all probably being paid six figures and are paying lots of tax," he said.
"But we're withdrawing from it because of this absolutist position on the European Court. I think she could show some flexibility in that area and argue actually surely we want nuclear scientists to come to this country."
Mr Coates then asked: "Do you think if she moved on Euratom they'd be cheering around the Cabinet table?"
Mr Chapman replied: "I think they would be and I think if she doesn't shift on Euratom I think the Parliament will shift it for her."
It came as the Telegraph reported concerns in the City that Mrs May was not focusing enough on getting a good Brexit deal for Britain's financial services sector, compared with industries such as manufacturing or fisheries.
William Wright, the managing director of New Financial, a think-tank, told the newspaper: "The focus since the election has been on a free trade agreement for goods with UK politicians talking about German cars, Italian prosecco and French cheese.
"But the most complicated area of any future agreement with the EU will be services, especially financial services.
"Banks, asset managers and insurers will have to assume the worst-case scenario unless they get the answers they need in the next few months."
Liberal Democrat Brexit spokesman Tom Brake said: "When David Davis' ex-chief of staff is telling you your approach to Brexit is too inflexible, it might be time to think again.
"Theresa May has tied herself up in knots by setting so many red lines so early on in the negotiations.
"We need a cross-party Joint Cabinet Committee on Brexit to provide scrutiny and consensus in the national interest as we navigate these vital negotiations."