The tensions have arisen because the EU has made it clear it will refuse to sign an overall withdrawal agreement - paving the way for a transition deal and the opening of talks on an EU-UK trade deal - if the UK insists on specifying a date by which customs "backstop" arrangements created to prevent a hard border in Northern Ireland must end.
Under pressure from all sides, Theresa May told journalists at Downing Street reception that talks on the key issue of the Irish border were likely to continue until November, while cabinet ministers who met with May yesterday evening were cited by the Financial Times as saying the border issue was close to being settled.
As officials continued to wrangle over the precise wording of the agreement in Brussels, a Downing Street spokeswoman said the Prime Minister would "never agree to a deal which would trap the United Kingdom in a backstop permanently" and "our position is that this future economic relationship needs to be in place by the end of December 2021 at the latest".
International Development Secretary Penny Mordaunt and Leader of the Commons Andrea Leadsom - who, like Ms McVey, both backed Leave in the referendum in 2016 - were also said to harbour deep concerns.
Pensions secretary Esther McVey pointedly refused to endorse the PM's plan during the latest cabinet meeting and global development secretary Penny Mordaunt and the leader of the Commons Andrea Leadsom also made it clear they held deep concerns.
In a direct message to Mrs May, she urged her not to follow Margaret Thatcher in accepting a deal she later regretted - referring to the former prime minister's part in the Anglo-Irish agreement.
SNP Europe spokesman Stephen Gethins said the technical papers should serve as a "wake-up call".
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"What good are Boris and Davis doing shouting from the outside?"
"We are close, we are nearly there, we just need to be steady for a few more weeks and if we do that the prize is there to be grasped".
However, with just days to go until May's crucial summit with European Union leaders, ministers believe action must be taken now.
Jacob Rees-Mogg, chairman of the European Research Group of pro-Brexit MPs, warned that when it came to the backstop proposal "temporary means eternal".
Brussels and Dublin say if there's no deal then the north should share their regulations, remaining in the single market and the customs union, as this is the only way to avoid a hard border. It will come into effect at the end of the proposed transition period, in January 2021, unless a new trading arrangement which protects the open Irish border is in place.
The potential extension of the transition period, which could see the United Kingdom stay in the EU single market and customs union, accept continued free movement and make further payments to Brussels, is being considered as intensive negotiations continue ahead of the European Council summit. Cabinet Brexiteers are just about willing to accept this, as long as the backstop comes with a fixed endpoint - for example:;it would cease on on January 29, 2023.
DIT said that, in its preparations for Brexit, it is seeking to forge new bilateral deals with 70 countries now covered by European Union trade agreements which will be "identical or substantially the same" as those Britain is giving up.