The prime minister will hold an extended discussion on Brexit at the cabinet meeting on Tuesday, the eve of her trip to Brussels, where she hopes to outline a compromise deal on the Irish border.
DUP leader Arlene Foster insisted on Tuesday that her party would not accept customs or regulatory checks on goods travelling in either direction between Northern Ireland and Great Britain after meeting European Union chief negotiator Michel Barnier in Brussels.
She praised the former foreign secretary for his "positive" views on Brexit, as Mr Johnson pushes for a Canada-style trade deal with the European Union instead of Mrs May's Chequers plan, which he argues is only partially leaving the bloc.
Top EU officials were warned Wednesday to make plans to cope with the fallout from a "no-deal" Brexit as their chief negotiator said talks with Britain must make more progress before next week's crunch summit.
It highlights how Theresa May's "precious Union" has little meaningful support among the British prime minister's own supporters or those in other parties who regard themselves as unionist.
A Brexit sign is seen between Donegal in the Republic of Ireland and Londonderry in Northern Ireland at the border village of Muff, Ireland, February 1, 2018.
Barnier said Brexit would trigger the need for customs, Value-Added Tax and compliance checks with EU standards between Ireland and Northern Ireland in the event that a planned "backstop" were triggered because a future EU-UK trade deal was not sufficient in itself to ensure the land frontier was not a "hard border".
- Treasury minister John Glen backed a previous prediction by the Bank of England that around 5,000 financial services jobs will have been shifted out of London by "Day One" on March 29.
But with both sides confirming that differences remain on issues such as the status of the Irish border, expectations are growing that the final moment of decision will be put back to a special summit in November.
The Budget is due on October 29, after the next European Union summit and before any special Brexit summit that is expected to finalise the deal.
Foster stressed that she wants to reach a Brexit deal and she is staying in Brussels for the next two days in order to try and find a solution that would be acceptable to her. If they jump the gun at the Budget before the Withdrawal Bill votes later, they're playing very hard ball indeed - and before they can know exactly what's going on in Brussels.
But Mr Barnier's comments suggest there is still a long way to go before the crucial issues are settled.