British opposition leader Keir Starmer has promised to improve the country's trading relationship with the European Union in 2025 if his Labour Party wins the next election.

Starmer told the Financial Times he would seek closer ties with the bloc when the partnership comes up for review in 2025 but reiterated that he did not want to take Britain back into the single market or customs union.

Instead, Labour would seek to improve the 2021 Trade and Cooperation Agreement (TCA) struck by former British Prime Minister Boris Johnson. The FT said Starmer talked about wanting closer ties in areas such as security, innovation and research.

Labour has long said it wants better relations with the EU, including a deal that would cut the need for checks and paperwork for animals and some foods, plus closer ties in professional and financial services.

But the party says it will not renegotiate the TCA, only improve it.

"Almost everyone recognises the deal Johnson struck is not a good deal - it's far too thin. As we go into 2025 we will attempt to get a much better deal for the UK," the FT quoted Starmer as saying.

The Bank of England has said Brexit has reduced the capacity of Britain's economy to grow, weighing on investment and productivity.

Earlier this year, the BoE's deputy governor Ben Broadbent said the impact of leaving the EU had fed through into the economy faster than the central bank had expected, although the effects had not been larger than anticipated.

Labour has a roughly 20 point lead in opinion polls over Prime Minister Rishi Sunak's Conservative Party before an election expected next year.

Polls also show most British people think Brexit was a mistake. However, Starmer is under pressure to strike the right balance between seeking better economic ties without handing firepower to Brexit supporters and critics who accuse him of wanting to reverse the 2016 Brexit referendum.

Britain's pensions minister Laura Trott said on Monday Starmer had changed his position on Brexit multiple times, including previously pushing for a second referendum.

"I think the question is, what price is he willing to pay to reopen that trade deal? And it's something that I'm very concerned about," she told LBC Radio.

(Reporting by Kate Holton and Kylie MacLellan; Additional reporting by Rishabh Jaiswal in Bengaluru; Editing by Sandra Maler and Andrew Cawthorne)