Boris Johnson has been warned by senior figures in Brussels that failing to pay the £39 billion divorce bill would damage relations between the UK and the European Union and jeopardise future trade talks.
But officials in Brussels said the UK must honour commitments made during its EU membership and pointedly said that “settling accounts is essential to starting off a new relationship on the right foot”.
On Sunday, Mr Johnson told ITV News Political Editor Robert Peston if the UK left without a deal then the £39 billion "is no longer strictly speaking owed".
He said: "I'm not going to get into the figures, but there will very substantial sums available to our country to spend on our priorities, to spend on getting on getting our businesses ready.
"It's not a threat, it's a simple statement of reality, that's the way things are."
But, just 24 hours later, Guy Verhofstadt, the European Parliament’s Brexit co-ordinator, warned Mr Johnson there would be trouble ahead if that account was not settled.
He said: “If the UK doesn’t pay what is due, the EU will not negotiate a trade deal.
“After a ‘no deal’, this will be a first condition of any talks. Britain is better than this.”
European Commission spokeswoman Mina Andreeva said: “All commitments that were taken by the 28 member states should be honoured and this is also and especially true in a no-deal scenario where the UK would be expected to continue to honour all commitments made during EU membership.
“Rather than going now into a judicial action threat, I think it is important to make clear that settling accounts is essential to starting off a new relationship on the right foot based on mutual trust.
“I would also say that as far as I understand this issue has not been raised with the EU side, for the time being, officially.”
Mr Johnson said on Sunday that there would be “very substantial sums” available from the £39 billion to spend on domestic priorities if there was a no-deal Brexit.