Theresa May is facing criticism from her own party after signalling she might be willing to extend the post-Brexit transition period.
Scottish Secretary David Mundell is said to have written to her to condemn the move, whilst former leader Iain Duncan Smith said it would see the UK paying the EU “tens of billions” more.
Mrs May will pitch her vision for a post-Brexit UK to Asian leaders later.
The current plan is for a transition period of 21 months to smooth the path from Brexit to the UK and EU’s future permanent relationship.
But with the two sides failing to reach a deal yet after an EU summit of all its leaders this week, Mrs May said this arrangement could be extended “for a few months”, if needed.
She also said it could be a “further solution” to the search for a “backstop” to ensure no hard border in Ireland – the major sticking point in negotiations.
EU Council president Donald Tusk said he was “sure [EU] leaders would be ready to consider [an extension] positively” if the UK wants it.
The PoliticsHome website reports that Mr Mundell has become the first cabinet minister to “break ranks” with his letter to the PM, warning against the extension if it means forcing the UK to continue to abide by EU fishing rules for longer.
Prominent Brexiteer Mr Duncan Smith told BBC’s Newsnight he could not understand an extension when the UK “still hasn’t got anything back in return” and said the negotiations “look more like a capitulation”.
He also claimed the move would see the UK having to pay into the EU’s next budget, adding: “It would be very hard to tell the British people that we are extending another year or more into the implementation phase, and we’re then going to pay tens of billions of pounds over when we actually say we need it for other domestic programmes.”
Backbencher Johnny Mercer was harsher with his assessment, describing the government as a “shit show”.
In an interview with The House magazine, the former Army officer said he would not have stood as an MP “if the situation was like it is now” and that he was no longer sure that his “set of values and ethos” were still “aligned with the Conservative Party”.
What is the issue?
The UK is due to leave the EU on 29 March 2019, and the transition period, which Mrs May prefers to call the implementation period, is designed to smooth the path to a future permanent relationship.
During this transition period, which is due to finish on 31 December 2020, the UK’s relationship with the EU will stay largely the same.
The UK has signed up to the principle of agreeing an Irish border “backstop” – an insurance policy designed to prevent the need for customs checks – in case there is a gap between the transition period and the future permanent relationship coming into force.
The problem is that the two sides have yet to agree what form the backstop will take, and how long it could last.
On Thursday. the plan received condemnation from members of Northern Ireland’s Democratic Unionist Party – whose support the government needs in key votes – saying it would not change the “fundamental problem” with the EU’s backstop plan.
This is because it involves Northern Ireland staying aligned to EU rules, which the DUP – and the UK government – says is unacceptable because it creates a new border in the Irish Sea.
Brexiteers were also not impressed, with Conservative backbench MP Jacob Rees-Mogg telling Sky News it was “a rather poor attempt at kicking the can down the road”.
And Remainers were unhappy too, with former minister Nicky Morgan saying an extension would be “unhelpful” and would leave the UK in a “Brexit holding pattern”.
Asked earlier whether he would support a longer transition period, Labour leader Jeremy Corbyn said: “The prime minister has got herself into this mess by failing to reach any meaningful agreements with the EU”.