Sky News has learnt that the cabinet agreed the prime minister should adopt bolder language when she travels to Brussels to flesh out the political declaration on the future relationship between the UK and EU.
The current document is just seven pages long, but senior ministers were shown a secret 20-page draft that will form the basis of a key meeting between Jean-Claude Juncker, president of the European Commission, and Mrs May on Wednesday.
It comes as the PM felt the first effects of the DUP’s promise not to expect “business as usual”, with the government forced to adopt four amendments to a crucial finance law after the Northern Ireland party withdrew its support.
The DUP, which is propping up Mrs May’s government with a confidence and supply deal, is supposed to support her on laws including “finance bills”.
In a two-and-half-hour cabinet meeting ahead of Mrs May’s meeting with Mr Juncker, her top team agreed she should ask the Commission to guarantee the future trade relationship between the UK and the EU should be “at least as good as it gets” to the best free trade deal.
This is more ambitious than the current language, which suggests the UK should seek a trade deal at an “equivalent” level to other third party countries.
“The more flesh we can put on the bones, the better. It will mean more things to more people and we can take more of the party with us,” one senior government source said.
Mrs May’s cabinet also agreed that the prime minister should seek to formally insert the principle of using technological options for managing the Irish border into the future declaration as she enters into final talks with Brussels.
The PM told her cabinet on Tuesday she was exploring alternatives solutions to maintain a soft border on the island of Ireland as she seeks to stave off a confidence vote from mutinous backbenchers.
However the late stage changes to the text mean that Mrs May might not be able to seal the agreement on Sunday, with more time needed to work through some of the technicalities, according to two senior sources.
“We can have another summit the following week if necessary,” one senior government figure said.
EU leaders are due to meet Mrs May in Brussels on Sunday to approve the Brexit withdrawal agreement and a political declaration on future EU-British relations.
Meanwhile, Labour claimed “the government have in effect collapsed” and that Mrs May is “in office but not in power”.
John McDonnell, the shadow chancellor, tweeted that the passing of four amendments to the finance bill was “absolutely staggering”.
Ministers will now be forced to publish a review on the public health effects of gambling, and reports on tax avoidance and evasion.