Sir Keir Starmer has said he will seek a “much better” Brexit deal with the EU if Labour wins the next general election.
The opposition leader told the Financial Times that the current deal, which is due for review in 2025, is “too thin”.
Sir Keir was speaking at a conference of centre-left leaders in Montreal, Canada.
But he ruled out re-joining the customs union, the single market or the EU.
It remains unclear, however, if Brussels would be open to making major changes to the agreement, which was agreed by former Conservative Prime Minister Boris Johnson in 2021.
Sir Keir has repeatedly said he would not seek to rejoin the EU if his party comes to power, promising to “make Brexit work”.
His party has consistently held double-digit leads in the political opinion polls, with a general election expected to take place some time in 2024.
“Almost everyone recognises the deal Johnson struck is not a good deal – 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 said, although he did not specify what parts of the deal he would seek to improve.
He added that he was confident a better deal could be negotiated with Brussels, as well as a “closer trading relationship”.
“We have to make it work. That’s not a question of going back in, but I refuse to accept that we can’t make it work,” he said, adding that he was thinking about “future generations”.
“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.”
The Labour leader spent the weekend meeting fellow centre-left leaders in Canada, including the country’s prime minister Justin Trudeau.
He is also expected to travel to Paris to meet French President Emmanuel Macron later this week, where post-Brexit relations are expected to feature heavily in talks.
He also travelled to the Hague, the Netherlands, last week to meet with the EU’s law enforcement agency Europol, seeking a deal to try and stop smuggling gangs bringing people across the channel in small boats.
That led to accusations by Prime Minister Rishi Sunak and Home Secretary Suella Braverman that his party was planning to let the UK become a “dumping ground” for 100,000 migrants from the continent each year, claims he said were “complete garbage”.