Moody’s Investors Service has said the probability of the UK walking away from the European Union (EU) without a deal is “substantial”, as EU negotiators threaten to stall talk until the UK agrees to pay a 50 billion euro divorce bill.

“We still think that the EU and the UK will eventually come to an agreement that captures many, but not all, of their current trade arrangements,” said Colin Ellis, the credit rating agency’s managing director of credit strategy.

“But the probability that negotiations will fail and no agreement will be reached is substantial,” he added.

Many committed Brexit supporters believe that walking away from the bloc without a trade deal (and reverting to World Trade Organization rules) will be a good outcome, giving maximum control of laws and trade to the UK.

Even Prime Minister Theresa May, who campaigned against Brexit, famously said that “no deal is better than bad deal” for the UK, and implied a trade war could ensue if the EU was not prepared to compromise.

The Moody’s warning came after the second day of Brexit negotiations in Brussels, where EU diplomats said the bloc’s chief negotiator, Michael Barnier, could threaten to “stall” negotiations if the UK does not make a serious offer on the so-called “Brexit bill”.

“Financial settlement is the priority,” one EU diplomat said told the Politico website. “The EU will not walk away from talks but will stall them”, the diplomat said, adding: “The impression we got so far is that the U.K. is not ready for these talks.”

Another EU diplomat said: “It is reasonable to expect the Brits to say something other than ‘we will not pay a penny.’ If that’s not the case, what is there to talk about?”

Last week, Foreign Secretary Boris Johnson told the House of Commons the EU could “go whistle” if it expected the U.K. to pay the massive bill.

Mr. Barnier had initially demanded the UK pay a £51.2 billion (€60 billion) divorce bill, reportedly raising it to 100 billion euros in May, and has said talks on trade could not begin until December unless the bill was resolved.

However, during talks yesterday, he softened this position, by discussing the future of EU import quotas for after the UK leaves the bloc.