Britain will face EU demands for billions of euros in cash if it fails to strike a Brexit deal, Brussels officials and diplomats said on Monday after talks with London stalled 18 days before it is due to leave the bloc.

Prime Minister Theresa May agreed a withdrawal treaty last year under which Britain would pay the European Union close to 50 billion euros over the coming years to meet commitments made while a member. But the British parliament has rejected the deal and the treaty will be void if nothing changes by March 29.

In the event of a “no-deal” exit, likely to cause economic disruption, the EU would insist on Britain settling those financial commitments – a significant part of the EU budget – before any resumption of discussions, which both sides see as inevitable, on how to manage trading relations in the future.

With May planning to put the package to a second vote in the House of Commons on Tuesday, her negotiators failed to secure concessions in Brussels at the weekend and EU officials and national diplomats told Reuters they were growing pessimistic and looking at how a collapse of talks might play out.

An assumption in Brussels that May would ask for and get a delay to the deadline of a few weeks is in question: “We really want to be over with it now,” one official said. “It’s not going anywhere so even an extension is unlikely to break the impasse.