The UK will not accept a Brexit deal that involves being indefinitely locked into a customs union with the EU, Dominic Raab has said.
Britain’s Brexit Secretary said a provision on a customs union which was not "finite" would fail to deliver the result of the 2016 referendum.
Downing Street has insisted that Prime Minister Theresa May would never agree a Brexit deal with the European Union which "traps" the UK permanently in a customs union.
The pledge came amid speculation over possible ministerial resignations if Mrs May gives too much ground ahead of a crunch Brussels summit next week.
European Commissioner Guenther Oettinger said "it does appear possible there will be a breakthrough" at the 17-18 October summit, fuelling speculation a deal is near on a so-called "backstop" for the Irish border.
It is understood that a number of ministers voiced concern at a meeting with Mrs May yesterday that any such backstop could leave the UK in an open-ended customs union, preventing it from seeking trade deals elsewhere in the world.
Mr Raab said: "It would have to be finite, it would have to be short and it would have to be, I think, time-limited in order for it to be supported here.
"What we cannot do is see the UK locked in via the backdoor to a customs union arrangement which would leave us in an indefinite limbo. That would not be leaving the EU."
Chancellor Philip Hammond became the first senior British government figure to suggest that the backstop - designed to keep the border between Northern Ireland and the Republic open in the case that no broader EU/UK trade deal is finalised - will "probably" have to come into effect for a period.
Nigel Dodds, deputy leader of the DUP, said he expected developments over the weekend "in terms of the government's own position and the cabinet".
The DUP is adamant it will not agree to anything which results in imposition of extra customs or regulatory checks between Northern Ireland and the rest of the UK.
Mrs May 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.
However, the EU is mounting resistance to any specific time limit being included in the text of the UK's Withdrawal Agreement while Leave-backing ministers are understood to be insistent that the end of the arrangement should be more precisely defined than the vague term "temporary".
Tánaiste Simon Coveney has insisted the backstop should be able to remain in place "unless and until something better comes along" and told ITV News it was a "deal breaker".
Downing Street has always been clear that it does not wish or expect the backstop option to be implemented, as it insists 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.
However, Mr Hammond 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."