Theresa May has been warned not to attempt to force through a "soft" Brexit deal which would keep the UK closely tied to Brussels.
The Prime Minister is trying to find a compromise that will secure support from both wings of her Cabinet at a meeting on Friday, but critics called for the Government to maintain its red lines on leaving the single market and customs union.
A group of more than 40 Eurosceptic Tories met Chief Whip Julian Smith to air their concerns about the prospect of a soft Brexit which would restrict the UK's freedom to diverge from EU rules in future.
Jacob Rees-Mogg, chairman of the European Research Group (ERG) of pro-Brexit Tories, said: "I won't be reassured until I know the details of what comes out on Friday, one way or the other."
In an attempt to address concerns, Mrs May said at Prime Minister's Questions the Government would ensure "we are out of the customs union, that we are out of the single market, that we are out of the jurisdiction of the European Court of Justice, we are out of the Common Agricultural Policy, we are out of the Common Fisheries Policy, we bring an end to free movement, we take control of our borders, we have an independent trade policy".
Her comments came after Mr Rees-Mogg hit out at reports suggesting the meeting of Cabinet ministers at Chequers would be asked to support close continued alignment on rules for goods and tariffs.
"It's hard to think of a worse idea," he told the BBC's Daily Politics.
Adopting EU tariffs would be "abandoning the benefit of Brexit" and "a really foolish policy" because it would curtail the UK's ability to strike its own trade deals.
Asked if he would be prepared to rebel if the Cabinet's conclusions at Chequers were unacceptable to him, Mr Rees-Mogg said: "If the agreement from the Cabinet is that we will give the EU £39 billion merely on good faith of the EU's negotiating a trade deal, I will vote against that. I don't think I can be clearer than that."
In a sign of the tensions within the Tory ranks, one MP said a meeting of the ERG on Tuesday night was the "angriest" he had ever been to "even stretching back to Maastricht" - referring to the bitter battles fought during John Major's premiership.
The subsequent meeting with the Chief Whip was used by the ERG MPs to spell out their demands for the forthcoming White Paper, stressing that there must be no watering down of the position set out in the Conservative manifesto.
There was also widespread concern among the MPs about the role being played by Olly Robbins, the Prime Minister's Europe adviser and the senior official involved in negotiations with Brussels.
And there were demands for a greater emphasis to be placed on preparing for a "no deal" Brexit.
Tory MP Andrea Jenkyns urged Cabinet Brexiteers to stand up for Leave voters - and referred to the jockeying for position to succeed Mrs May.
In a message on Twitter aimed at Mr Johnson, Mr Gove, Penny Mordaunt, Liam Fox, Andrea Leadsom and Chris Grayling, she urged them to "show your steel on Friday".
"We know some of you want to be the future party leader," she said.
Eurosceptics fear the Prime Minister will set out plans for a soft Brexit in order to overcome the problems at the Irish border and ports across the UK if there were customs or regulatory barriers to trade.
Ms Jenkyns warned the Prime Minister's position would be under threat if she opted for a Norway-style relationship with the EU inside the single market.
"If we don't deliver Brexit, if we're half in and half out, it's going to be catastrophic for the Conservative Party," she told the ConservativeHome website.
"They're not going to trust the party. In our manifesto, all of us, Brexiters and Remainers, we stood on that manifesto that we would deliver Brexit."
She added that "history shows, prime ministers keep their jobs if they keep their promises".
Brexiteer Cabinet minister Michael Gove insisted that a "united position" would be reached at the away day, ahead of the publication of the White Paper next week.
And he played down speculation that pro-Brexit ministers such as Foreign Secretary Boris Johnson could quit if there was perceived to be backsliding over the break from Brussels.
Insisting that the red lines remained intact Mr Gove said: "The Prime Minister has a clear plan which will ensure that Britain can leave the EU, be outside the single market and customs union, maintain as frictionless access as possible to the European market and also ensure that we take back control of our laws and our borders."
Asked about the possibility of people quitting as ministers after Friday's showdown, Mr Gove told BBC Radio 4's Today: "The only departures that I think we will see are more departures from Heathrow when a third runway is built."