European Union officials put the odds of British Prime Minister Theresa May reaching a deal with Brussels on the Irish border at “50-50”.

This week, Brexit negotiations between the British government and the European Commission’s taskforce, led by Michel Barnier, are slated to enter a secretive phase known as the “tunnel”.

According to The Guardian, however, senior EU figures involved in the talks warned the competing redlines remain “incompatible” in key areas.

The British government has set out its stall to make “decisive progress” on the issue of the Northern Ireland backstop by Friday, in the hope that Donald Tusk, the president of the European council, could then call an extraordinary Brexit summit for the end of the month to seal the deal.

“We are not sitting on powder keg knowledge that we have signed a secret deal,” one No 10 source was quoted as saying by The Guardian. “We are not on the cusp of some seismic shift.”

Some at the highest levels of government fear that, unless progress is agreed by November 6 when the May sees her senior ministers and parliament breaks for recess, the cabinet may not have a direct input before a summit announcement is made.

“The reality is that we need a November summit more than the EU do,” a government source said. They suggested that a December deal would mean not only a later parliamentary vote but would require spending on no-deal planning and changes to the roles of hundreds of civil service.

Brussels has so far insisted the withdrawal agreement must contain legal text that could keep Northern Ireland in effect in the customs union and single market as Britain leaves.

According to The Guardian, one EU official suggested that such a UK-wide customs deal could only replace the Northern Ireland-specific text if it was a permanent arrangement, and even then, there would serious legal issues with making such a commitment at this stage.

“There is an evolution in the commission’s thinking. From what they originally proposed, there is a shift towards the UK in terms of the UK-wide thing so, yes, flexible, but whether that flexibility will lead to agreement is something else,” the official said.

The source said any hope of Northern Ireland-specific customs arrangements being removed would involve a “huge jump on the UK side”.

What is more, the same official suggested that May would need to make a “calculation about what is sellable and how she sells it, but it does not correspond to the buccaneering Britain of Bojo [Boris Johnson]”.