However Brexiteers - including Brexit Secretary Dominic Raab - are insisting any arrangement which would see the United Kingdom effectively remain part of the customs union while negotiations over a free trade deal take place must be strictly time-limited - something the EU has been resisting.
Britain's Prime MinisterTheresa May attends a roundtable meeting with business leaders whose companies are inaugural signatories of the Race at Work Charter at the Southbank Centre in London, Britain, October 11, 2018.
The Former Labour Prime Minister also said Theresa May is unlikely to get her Chequers Brexit plan through parliament, urging Labour MPs to vote against it.
Barnier said Brexit would trigger the need for customs, Value-Added Tax and compliance checks with EU standards between Ireland and Northern Ireland in the event that a planned "backstop" were triggered because a future EU-UK trade deal was not sufficient in itself to ensure the land frontier was not a "hard border".
Earlier on Thursday, May told Northern Ireland journalists that Irish border talks would likely continue until November.
And she again rejected any suggestion the north should remain within the single market, accusing Brussels of wanting to "place an effective one-way turnstile from Northern Ireland into the rest of the United Kingdom".
His constituency contains the port of Larne, identified by European Union chief Brexit negotiator Michel Barnier as a place where checks on animals and animal products from Great Britain into Northern Ireland could be intensified in order to prevent a hard border with the Republic of Ireland.
"Trade from Great Britain into Northern Ireland would be in danger of restriction". While London wants to regulate that by a future trade deal with the European Union, the bloc insists on an emergency fix in case negotiating new relations takes longer, or fails.
Arlene Foster, the DUP leader, said on Thursday afternoon that the prime minister could not "in good conscience" recommend such a deal and vowed to oppose it. Britain's Brexit minister, Dominic Raab, could also come to Brussels then if weekend talks cover enough ground.
Speaking after her Brussels meeting, Mrs Foster refused to play down the growing rift between her party and the ConservativeGovernment. She'd be ripping up her guarantee to support the PM in the commons.
It comes as Brexit negotiations enter what is being referred to as a "tunnel phase", with no publication of the British or European Union position on the backstop to be published until it is agreed. "Without an end date, we could be in the customs union forever".
He added that the DUP could vote down the Budget but still support the government in a confidence vote, as long as it changed its approach to Brexit.
A functioning Northern Ireland executive could have an impact on the final terms of any Brexit deal, she emphasised.