The chancellor has risked angering cabinet ministers who oppose removing the time-limit on the United Kingdom remaining in the European Union's customs territory by demanding close link to Europe even after 2020.
Ahead of a crucial Brussels summit next week, British and European Union officials are working through the weekend to try to resolve their differences amid optimism that the distance between the sides is narrowing. "So process is a lot more positive this week - substance still very challenging".
"This isn't just one more little compromise from the prime minister to get a deal over the line.it is the litmus test for the taking back control. this is the killer moment", a Cabinet source told BI.
Britain warned on Friday that leaving the European Union without a deal would mean drugmakers needing to stockpile experimental treatments in case of border delays.
London has published more than 25 technical notices covering issues from consumer rights and sanctions policy to rail transport and taking horses overseas.
The customs union proposal was advanced by Brussels as a way of keeping the Irish border open if no definitive trade deal is reached.
May's Northern Irish supporters vehemently oppose any checks between the province and mainland Britain after Brexit. It is now due to expire in December 2020.
The EU has proposed keeping Northern Ireland in the customs union if a UK-EU trade deal can not be done in time.
Companies operating electricity interconnectors, which include Britain's National Grid NG.L and French grid operator RTE, should "carry out contingency planning for a "no deal" scenario", a government paper said.
"The prime minister would never agree to a deal which could trap the United Kingdom in a backstop permanently", May's spokeswoman said on Friday.
They added that to wait until Tuesday's Cabinet meeting and somehow "bounce" ministers into supporting her deal would be "the worst possible way of doing it".
Her party has threatened to cause a political crisis by voting down Philip Hammond's Budget if Mrs May gives way to Brussels and Mrs Foster said: "The DUP's actions this week are not as some have suggested about "flexing muscle".
It confirmed if these are not in place in time for a no-deal Brexit, exports and imports to the countries will be subject to tariffs under World Trade Organisation rules. It said it was working hard to mitigate risks in these areas in case of a no-deal.
According to the BBC, Brexiteers were particularly concerned over the fact that Britain could be tied to the bloc's mechanisms indefinitely, which would become an obstacle to the country's independent trade deals elsewhere once it leaves the EU.