Keir Starmer has said he will seek a “better” deal with the EU if Labour wins the next general election.
The Labour leader said “almost everyone” recognises the agreement struck with Brussels by the Conservatives on leaving the EU was “not good”.
“It’s far too thin,” he told The Financial Times.
“As we go into 2025 we will attempt to get a much better deal for the UK.”
He was speaking at a conference of progressive leaders in Montreal, where he met Canadian Prime Minister Justin Trudeau and before a meeting with France's President Emmanuel Macron, as part of a flurry of overseas engagements designed to promote him as the UK’s prime minister in waiting.
Labour has long been critical of the deal negotiated by the Conservatives under Boris Johnson, with the Trade and Co-operation Agreement scheduled for review in 2025.
Mr Starmer told the newspaper it was an “important” moment to reset relations.
“We have to make it work. That’s not a question of going back in. But I refuse to accept we can’t make it work. I think about those future generations when I say that.
“I say that as a dad. I've got a 15-year-old boy and a 12-year-old girl. I'm not going to let them grow up in a world where all I've got to say to them about their future is, it's going to be worse than it might otherwise have been.
“I've got an utter determination to make this work.”
Labour has ruled out rejoining the customs union or single market, but Mr Starmer said he was confident a better deal could be negotiated with Brussels.
“I do think we can have a closer trading relationship as well. That's subject to further discussion.”
Mr Starmer earlier said it was “complete garbage” to suggest Labour planned to join an EU-wide migrant quota scheme as part of efforts to address small boat crossings in the English Channel.
Prime Minister Rishi Sunak and Home Secretary Suella Braverman claimed Labour planned to let the UK become a “dumping ground” for 100,000 migrants from the EU each year.
The political row emerged after Mr Starmer indicated he could be prepared to do a deal with Brussels which would involve the UK taking a quota of asylum seeker applicants who arrive in the bloc in exchange for the ability to return people who cross the English Channel.
“The idea that we're going to join the EU scheme on quotas is complete nonsense. We're not an EU member and that wasn't what I was talking about,” he told Sunday Morning with Trevor Phillips on Sky News.
Senior Labour MP and shadow minister Pat McFadden, questioned on the same issue on BBC One's Sunday With Laura Kuenssberg, said: “I don't think it's going to be an allocation of numbers; we're talking about individual cases where a child may have strong family links here.
“It's not 'we'll take this many, you take that many' – that's not the kind of negotiation we want to have.”
Labour is also facing renewed pressure from its main union backer Unite, which is reportedly set to launch a grass roots campaign to call for more radical policies on energy and steel.
Unite general secretary Sharon Graham, who has called for public ownership of energy and has been critical of Mr Starmer in the past, told The Guardian the union would be targeting “red wall” parliamentary constituencies as part of an effort to put pressure on the Labour leadership.