Theresa May should refuse to pay the money the European Union says Britain owes it in legally binding liabilities, Boris Johnson has said.
The Foreign Secretary said the PM should follow the example of Margaret Thatcher over the Brexit bill, which is estimated to be around £52bn.
Mr Johnson alluded to the former PM’s battle to secure a rebate for Britain from the EU’s budget in 1984, an achievement regarded by Eurosceptics as one of her finest moments.
“I think we have illustrious precedent in this matter, I think you can recall the 1984 Fontainebleau summit in which Mrs Thatcher said she wanted her money back and I think that is exactly what we will get,” he said.
The issue of the so-called “divorce bill” – intended to cover legally binding budget commitments already made by the UK – could be a major stumbling block in the negotiations after Ms May triggers Article 50.
The Prime Minister has pledged to invoke the treaty clause before the end of this month, starting the two-year countdown to Brexit.
The European Commission's chief negotiator Michel Barnier has reportedly discussed the figure of the liabilities with European leaders ahead of the crucial talks.
But Mr Johnson told BBC2’s Brexit: Britain’s Biggest Deal programme: “It is not reasonable, I don't think, for the UK having left the EU to continue to make vast budget payments. I think everybody understands that and that's the reality.”
In a sign of the pressure Ms May will face on the issue, Irish Prime Minister Enda Kenny indicated on Thursday that he would back demands for Britain to pay a divorce fee.
As he arrived at the European Council summit in Brussels, he said: “When you sign on for a contract you commit yourself to participation. And obviously the extent of that level of money will be determined.”
Brexit Secretary David Davis told the BBC programme 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.
He 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.
“You contemplate things so that you avoid them or you mitigate them,” he said.
Additional reporting by PA