Video report by ITV News Correspondent Angus Walker
Theresa May has faced fresh warnings of a rebellion from pro-Brexit MPs as she prepares for two days of crunch talks with senior ministers next week on the UK's future relationship with Europe.
Backbencher Bernard Jenkin warned the Prime Minister may see defections that would leave her without a majority in parliament if she does not commit the UK to leaving the single market and the customs union.
There were also reports in the Sunday Times that Brexiteers are mulling a leadership "coup" if they are not appeased in an ongoing split between hard and soft Brexit supporters within the party.
The right wing of the party is said to be considering an alternative top team that would see Boris Johnson as Prime Minister with Michael Gove as deputy and Jacob Rees-Mogg installed as Chancellor.
However, key May ally Amber Rudd dismissed reports of a leadership challenge and insisted the Cabinet would be able to command broad support for their blueprint on a final deal.
"I have surprise for the Brexiteers which is the (Cabinet) committee that meets in order to help make these decisions is more united than they think," she told BBC1's The Andrew Marr Show.
"We meet in the committee. We meet privately for discussions. I think that we will arrive at something which suits us all.
"There will be choices to be made within that but we all want the same thing which is to arrive at a deal which works for the UK."
Housing minister Dominic Raab insisted, "I think we've been very clear from the start - we are leaving the customs union".
He said there was "not a fag paper" between the members of the Cabinet on how they will approach the terms of the final exit deal with regards to freedom to organise trade deals with third party countries.
Meanwhile, the Liberal Democrat leader Vince Cable accused Jeremy Corbyn of acting in "collusion" with the Conservatives to enable Brexit to happen.
He said there was a "simmering anger" in the Labour ranks at their leader's failure to oppose Britain's withdrawal from the EU as he insisted that it was not yet a done deal.
He predicted that Mr Corbyn would eventually be forced to back a second referendum on the final Brexit deal with Brussels.
The latest clashes between politicians over Brexit came as a former Whitehall mandarin said that attacks on the objectivity of the civil service over forecasts were "completely crazy".
On Saturday, Mr Rees-Mogg accused Treasury officials of "fiddling the figures" to show that Britain would be worse off outside the EU, whatever the outcome of the negotiations.
But Gus O’Donnell, a former head of the Civil Service, told Peston on Sunday it was a case of shooting the messenger.
“Sometimes, you get these attacks because they just don’t like the message," he said.
"If you're selling snake oil, you don't like the don't like the idea of experts and testing your product.
Lord Turnbull, a former cabinet secretary and head of the civil service, went further in an article for the Observer in which he said the attacks were similar to those adopted by right-wing German nationalists in the 1930s..