THERESA May has told Brussels that Britain will “not pay huge sums of money” into EU coffers post Brexit after Boris Johnson urged her to channel the spirit of Margaret Thatcher into her negotiations with the other 27 member states.

Speaking at what is thought will be her last pre-Brexit EU summit, the Prime Minister declared: “Let me be very clear there is only ever one Margaret Thatcher.”

She then added: “If it comes to the issue of the comments about paying money into the EU, Boris is clear and I am clear when people voted on June 23 for us to leave the EU, they voted for us in the future not paying huge sums of money into the EU every year and, of course, when we leave the EU that will be the case.”

Mrs May spoke as speculation is high that – if the Lords back down early next week and accept the Commons will on the Brexit Bill – she could trigger Article 50 by as early as Tuesday or Wednesday.

Mr Johnson made his remarks as pressure mounted on the PM over a Brexit "divorce bill," which, it has been suggested, could total as much as £52 billion.

Enda Kenny, the Irish Taoiseach, indicated he would back demands for Britain to pay for leaving the Brussels bloc.

In an interview with the BBC, the Secretary of State suggested Mrs May should be inspired by Mrs Thatcher's battle to secure a rebate for the UK in 1984; regarded by Eurosceptics as one of her finest moments.

"We have illustrious precedent in this matter,” Mr Johnson declared. “You can recall the 1984 Fontainebleau summit in which Mrs Thatcher said she wanted her money back and that is exactly what we will get."

The issue of an exit fee for Britain could be a major stumbling block in the negotiations after Mrs May triggers Article 50, starting the two-year countdown to Brexit.

Michel Barnier, the European Commission's chief negotiator, has reportedly discussed the fee figure already with European leaders ahead of the crucial talks. He has revealed that he has agreed a "common position" on the budget regarding Brexit with Rumen Radev, the Bulgarian President, whose country will hold the rotating EU presidency for the first half of 2018; potentially a crucial period in the negotiations.

Any Brexit fee would cover legally binding budget commitments already made by the UK that will continue after withdrawal as well as pension payments for EU officials.

But Mr Johnson told BBC Two's Brexit: Britain's Biggest Deal: "It is not reasonable, I don't think, for the UK having left the EU to continue to make vast budget payments. Everybody understands that and that's the reality."

But in a sign of the pressure the PM will face on the issue, Mr Kenny made clear that he would back demands for Britain to pay a divorce fee.

"When you sign on for a contract you commit yourself to participation and, obviously, the extent of that level of money will be determined," he argued.

Meantime in the BBC programme, David Davis revealed that he had told Cabinet colleagues to work on "Plan B or C" if the UK failed to secure a favourable deal with Brussels during the negotiations on divorce and a future trade agreement.

The Brexit Secretary said it was "not a catastrophe to contemplate things" but insisted that a trade deal - "Plan A, or some variant of it" - was the most likely outcome of the talks.

At the end of February he explained that he had told senior ministers that their departments must prepare not only for Britain's "most important peacetime agreement" but also for "the unlikely scenario that no mutually satisfactory agreement can be reached".

Asked about the potential for the UK to walk away without a deal, Mr Davis said: "What I said to them was they've got to do the work for the so-called Plan B or C or whatever it is. It's not Plan A."

He added: "It's our responsibility as a government to make preparations for all possible outcomes. We're going in to a negotiation, we don't control the whole thing. By far and away the highest probability is Plan A, or some variant of it, namely a comprehensive free trade deal."

The Secretary of State insisted that it was sensible to consider what might happen if an acceptable trade deal was not on offer.

"You contemplate things so that you avoid them or you mitigate them," he said.

"If you went out on the street today and said to the ordinary member of the public, should the Government prepare for all outcomes, they would say of course." But he added: "I don't intend to go down that route. The aim of my department is to deliver Plan A."