Prime Minister Theresa May would never agree a Brexit deal that “traps” the UK in a customs union, Downing Street has said.
This came as Mrs May briefed key ministers on the latest developments in the Brexit negotiations in Downing Street on Thursday evening.
The Prime Minister set out in June proposals for a "temporary customs arrangement" to ensure that the border between Northern Ireland and the Republic remains open in the case that no broader EU/UK trade agreement has been finalised.
The document stated that the UK Government "expects" this arrangement to remain in place no later than the end of December 2021.
Specific time limit
British Prime Minister Theresa May arrives at the Council of the European Union on the first day of the European Council leaders' summit on June 2018
However the European Union is unwilling to have any specific time limit being included in the UK’s Withdrawal Agreement.
While the UK remains in a customs union with the EU, it cannot strike free trade deals with other countries outside of the bloc.
Brexiteers fear that once Britain is signed up to any sort of "temporary" arrangement, the UK will struggle to leave it in the foreseeable future.
As officials continued to debate over the wording of the agreement in Brussels, a Downing Street spokeswoman told a Westminster media briefing: "The Prime Minister would never agree to a deal which would trap the UK in a backstop permanently."
The spokeswoman said Mrs May stood by her proposals in June, adding: "Our position is that this future economic relationship needs to be in place by the end of December 2021 at the latest."
Downing Street has always been clear that it does not wish or expect the backstop option to be implemented, and that it will be possible to agree a wider trade deal guaranteeing an open border in Ireland by the end of the transition period in December 2020.
'Before we enter our long-term partnership'
British Prime Minister Theresa May speaks with Chancellor of the Exchequer, Philip Hammond
But Chancellor Philip Hammond has now suggested that he believes the backstop will "probably" be needed for a period.
He told Bloomberg TV: "We are not going to remain in anything indefinitely, we are very clear this has to be a temporary period.
"But it is true that there needs to be a period, probably following the transition period that we have negotiated, before we enter into our long-term partnership, just because of the time it will take to implement the systems required.
"It's very important to us that business doesn't have to make two sets of changes, that there will be effectively continuity from the current set-up through the transition period into any temporary period and then a single set of changes when we move into our long-term new economic partnership with the European Union."
Following Thursday's meeting of the "inner Cabinet" in Downing Street on Thursday, Government Chief Whip Julian Smith insisted ministers were united behind the Prime Minister
However, Work and Pensions Secretary Esther McVey, who was not at the Downing Street meeting, pointedly refused to endorse the Prime Minister's Chequers blueprint for Brexit.