The UK’s Brexit negotiator David Davis has described the deal struck by Theresa May to move to the next phase of talks as a “statement of intent”.
He said it was not “legally enforceable” and if the UK failed to get a trade deal with the EU then it would not pay its divorce bill.
But he stressed that the UK was committed to keeping a “frictionless and invisible” Irish border.
And it would “find a way” to do this if there was a “no deal” Brexit.
The Brexit secretary also stressed that the odds of the UK exiting without a deal had “dropped dramatically” following Friday’s joint EU-UK statement in Brussels.
And he spelled out the kind of trade deal he wanted with the EU, describing it as “Canada plus plus plus”.
Canada’s deal with the EU, signed last year, removes the vast majority of customs duties on EU exports to Canada and Canadian exports to the EU.
But Mr Davis said it did not include trade in services, something he wanted to see in the UK’s “bespoke” deal with the EU.
Chancellor Philip Hammond has previously suggested the Brexit divorce bill – which the Treasury says will be between £35bn and £39bn – will be paid even if no EU trade deal is struck.
Prime Minister Theresa May signed an agreement on Friday ruling out the return of a “hard border” on the island of Ireland, protecting the rights of EU and UK citizens and agreeing a formula for the divorce bill.
EU leaders are now expected to recommend starting the next phase of Brexit talks at a summit on Thursday.
But Mr Davis stressed Friday’s agreement was conditional on achieving an “overarching” trade deal with the EU, agreements on security and foreign affairs, as well as the two year transition period the UK wants after if officially leaves the EU in March 2019.
Friday’s agreement includes a fallback position if the UK fails to get a trade deal, which proposes full regulatory “alignment” between the EU and the UK.
This clause had been diluted at the insistence of the Democratic Unionist Party, which fears Northern Ireland would be separated from the rest of the UK, and move closer to Ireland, if it had to adopt EU rules to keep goods flowing across the border.
But there is still controversy, and confusion, over what “full alignment” would mean in practice, with some Brexiteers fearing the UK would have to continue to abide by EU regulations on agriculture and other issues after Brexit.
Mr Davis said: “I think if we don’t get a deal we’re going to have to find a way of making sure we keep the frictionless border – as it were an invisible border – in Northern Ireland.
“We do it at the moment. Understand something: at the moment there are different tax and levy regimes and excise regimes north and south of the border.
“We manage that without having border posts allotted along the 300 roads there and we will find a way of doing that.”
The UK’s opposition Labour party has ruled out remaining in the EU single market and customs union if it wins power.
But the party’s shadow Brexit Secretary Sir Keir Starmer said the party wanted a partnership with the EU that “retains the benefits of the single market and the customs union”.
Asked if Theresa May’s deal would mean Britain would stay very close to the single market and the customs union, he said: “Yes, and I think that’s the right thing and I think we should hold her to that because that goes to the heart of the question what sort of Britain do we want to be?
“Do we see Europe as our major trading partner in the future or do we want to rip ourselves apart from that?”
Asked if Britain would have to carry on paying some money in, he said: “Norway pays money in, they do it actually on a voluntary basis… there may have to be payments, that’s to be negotiated.”