Boris Johnson, one of the favourites to succeed outgoing British Prime Minister Theresa May, has said he will not pay the £39 billion so-called ‘Brexit bill’ that has been assigned to the UK if the EU refuses to provide another deal.

“I have always found it strange that we have to write the check before there is a deal,” says Johnson, in an interview with the Sunday Times. “I think our friends and partners need to understand that the money is going to be retained until such time as we have greater clarity about the way forward.”

Johnson adding it was “very strange” to write out the entire check before a conclusive deal can be signed. “Money”, he said, “is an excellent lubricant” when it comes to agreeing on a good deal.

A source close to French President Emmanuel Macron said that failing to pay the Brexit bill when the UK leaves the EU would amount to a sovereign debt default. “Not honouring your payment obligations is a failure to one’s international commitments. It is the equivalent of a sovereign debt default whose consequences are well known,” said a French official in reference to Johnson’s earlier comments.

Johnson, a former London mayor who served as May’s foreign secretary from 2016-2018, is the current clear favourite to win the Conservative Party leadership race after a recent opinion poll showed that the ex-parliamentarian and journalist with a commanding 43% lead over his nearest rival, Michael Gove, who is running a distant second with only 12% support.

Not paying the Brexit bill was just one of Johnson’s more notable proposals should he become the UK’s next prime minister. He also said he would abolish the Irish backstop agreement that would have seen Northern Ireland and Ireland maintain an open border after the UK quits the EU. Johnson would, according to his plan, continue to negotiate the status of the Irish border if the EU is willing to talk.

The contentious issue of the backstop has been one of the major stumbling blocks in the Brexit negotiations.

In the interview, Johnson also called himself the only one who could ‘beat the Brexit game’ set up by Brexit Party head Nigel Farage and Labour leader Jeremy Corbyn, whom Johnson compared to Scylla and Charybdis, mythical sea monsters mentioned by Homer in Greek mythology.