Britain could reportedly pay up to £36 billion to the European Union in a so-called Brexit divorce bill.
Tory Eurosceptics have insisted that the UK should not pay the fee following suggestions the Government might be prepared to offer the sum as part of a deal.
Whitehall sources have sought to play down speculation Theresa May would be prepared to pay a €40 billion bill in order to strike a comprehensive free trade agreement with Brussels.
Tory MPs warned that handing over money to Brussels after Brexit would be unacceptable to voters - with one suggesting Brussels should be giving money back to the UK instead.
The so-called divorce bill has been one of the main stumbling blocks in Brexit negotiations between the Government and Brussels.
The Sunday Telegraph reported that the Government will only agree to pay the sum if the EU treats it as part of a deal on future relations - including the comprehensive trade agreement sought by the Prime Minister.
The EU’s stance is that trade talks cannot begin until significant progress has been made on the financial settlement, citizens’ rights and Northern Ireland.
The newspaper quoted a senior Whitehall source as saying the EU’s position was that the fee should be 60 billion euro (£54 billion), but the “actual bottom line” was 50 billion euro (£45 billion); the UK’s position was 30 billion euro (£27 billion) and “the landing zone is 40 billion (£36 billion) even if the public and politicians are not all there yet”.
The proposal would see Britain offer to make net payments to the EU of some 10 billion a year for up to three years after Brexit as a partial down-payment on a final 40 billion euro settlement.
A senior Government source told the Press Association that “no such figure has been agreed” while another Whitehall source said it was “speculation”.
Conservative MP Peter Bone said a Brexit fee of that magnitude was unlikely to get through Parliament.
He said: “One of the prime reasons the UK voted to leave the EU was to stop sending them billions of pounds per year, so it would be totally bizarre to give the EU any money, let alone £36 billion, given also that over the years that we have been in the EU or its predecessor we have given them, net, over £200 billion.
“So if there was going to be any transfer of money then it should be from the EU to the UK.”
The Wellingborough MP said: “I think it would be very strange of Parliament to pay billions of pounds to leave an organisation that you have given hundreds of billions of pounds to and got nothing in return. That would be a very strange decision, so I don’t think it would happen.”
Jacob Rees-Mogg, MP for North East Somerset, said: “There is no logic to this figure, legally we owe nothing.”
Former Cabinet minister John Redwood told LBC Radio it was “completely ridiculous” to suggest the UK would have to pay to get Brussels to talk about trade because the EU “desperately” needed a deal.
He added: “Ministers would be quite wrong to be talking about any figures, we don’t owe them any money.
“It would be silly to be offering something when the EU is still not very willing to talk and is not coming up with anything constructive on its own side.
“The EU’s tactic is very clear. It’s divide and rule to try and get Britain negotiating with herself.”
Meanwhile Sir Vince Cable lashed out at hardline Brexit “martyrs” who view economic pain as a price worth paying to break away from Brussels.
His strongly-worded attack came after a YouGov poll suggested 61% of Leave voters would consider significant damage to the British economy to be a price worth paying for leaving the EU.
Writing in the Mail on Sunday the Liberal Democrat leader said: “To describe such masochism as ‘martyrdom’ is dangerous. We haven’t yet heard about ‘Brexit jihadis’ but there is an undercurrent of violence in the language which is troubling.”
Sir Vince, 74, added that the “self-declared martyrs” appeared to be “predominantly elderly”.
He said: “The old have comprehensively shafted the young. And the old have had the last word about Brexit, imposing a world view coloured by nostalgia for an imperial past on a younger generation much more comfortable with modern Europe.