A senior British official said that new, last-minute demands from the European Union negotiators have set back efforts to reach a trade deal in the next 48 hours.

Talks between the two sides are heading into a crunch period amid conflicting signs on whether a historic trade deal will emerge.

The EU’s chief negotiator, Michel Barnier, is poised to return to Brussels on Friday with diplomats saying the outline of an agreement could emerge by Saturday.

But the British official said the EU’s toughened stance had made a breakthrough in the next few days less likely. Another U.K. official said the change in the EU’s positions came in response to France’s warning on Wednesday that it could veto any agreement if it threatened its fishing industry.

One of the U.K. officials conceded that a breakthrough is still possible in the next few days.

It’s not unusual for assessments of the likelihood of a deal to gyrate wildly in the final days of a negotiation as both sides try to make the other blink. With the deadline looming to end the talks -- with or without a deal -- both sides are trying to heap pressure on the other.

Barnier has been locked in trade talks with his U.K. counterparts in London for a week and is now preparing to head back to consult on the final terms of a potential agreement with European Commission President Ursula von der Leyen and ambassadors from the bloc’s 27 member states, two people familiar with the situation said.

A final decision hasn’t been taken and developments in negotiations overnight could mean Barnier delays his return until Saturday, they said.

Johnson Call

It is likely that von der Leyen and Prime Minister Boris Johnson will hold a call on Friday or Saturday -- either to sign off on a deal or to give negotiators political instructions to try and finalize any agreement, the people said.

There has been progress on all of the three main disagreements that need to be resolved before a deal can be reached: access to British fishing waters, the competitive level playing field, and how the agreement is enforced. But none of them are settled yet.

Officials cautioned that negotiations were still at a very delicate stage and could fall apart at any moment. Equally, as tension mounts, last-minute problems could delay a breakthrough again.

Even after negotiators have agreed a deal, it would have to go before political decision-makers before it is formally announced. That means Johnson’s cabinet in the U.K. and, in Brussels, diplomats from member states and representatives from the European Parliament.

Once an accord is announced, all 27 of the EU’s political leaders, as well as the European Parliament, will need to approve it before it can take effect.