Britain "almost certainly" has a legal duty to pay a mega-billion divorce bill - even if no trade deal has been agreed at the end of Brexit negotiations, Tory MP Dominic Grieve has told ITV News.
The leading Remain-supporter rejected the claim of new Brexit Secretary Dominic Raab that Britain could threaten to forfeit payment of the £39 billion divorce bill if the EU fails to agree a new trade deal.
The former attorney general also warned of the "catastrophic" results of a 'no deal' Brexit scenario, saying medicines and food would quickly run out as "life as we understand it" would "grind to a halt".
Mr Raab earlier said there had to be "conditionality" under the Article 50 withdrawal mechanism between settling Britain’s exit payment and creating a new relationship with the EU.
- Video report by ITV News Political Reporter Daniel Hewitt
And in an interview with the Sunday Telegraph, he suggested the divorce bill could be used as leverage in talks.
But speaking to ITV News, Mr Grieve suggested that apparent bargaining power may be weakened by international legal requirements.
"It's true that the divorce bill is linked to the idea that we're going to have a framework agreement for the future," he said.
"But it's probably also right to say that as a matter of international law there is a divorce bill to be paid even if we don't have a future relationship."
Asked if that meant Britain has a legal requirement to pay, he replied: "Almost certainly yes, just as it's possible that there might be sums of money due to us on departure."
He added: "You can't just walk out on an international agreement and expect there not to be a settling of accounts."
Brussels has said a no deal scenario would mean there would be no specific arrangements in place for UK citizens living on the continent, or for EU migrants in Britain.
Mr Grieve told ITV News the impact on life in the UK would be enormous.
"A no deal would be catastrophic," he said. "If indeed we have no deal on anything life as we understand it in this country is going to grind to a halt."
Mr Grieve said his claim "might sound far-fetched" and added that he still anticipated 11th hour steps that could avoid the worst and create a temporary framework to enable trade to continue while permanent terms were decided.
But he said entering into such a state without arrangements would bring about an effective state of emergency.
"We would run out of medicines, we would probably run out of food fairly quickly because the food importations into this country are dependent on being a tariff-free access," he said.
"And if we haven't put in place the regulatory checks to enable that smooth flow to take place we're going to have miles of queues at Dover and at Calais."