Keir Starner is facing calls to act after Donald Trump cut off talks with Canada and threatened the Commonwealth country with more trade tariffs.

Just weeks before president Trump is due to meet King Charles, Canada’s official head of state, on a visit to the UK, he claimed he had “such power” over the country but added “I’d rather not use it.”

In a move that caused market turmoil amid fears of a renewal of Trump’s trade war, he said he would tell Canada the levies they will have to pay on goods entering the US “….within the next seven day period.”

The call for Starmer to intervene comes after a similar diplomatic row exploded earlier this year when the PM declined to back Canada against Trump’s ambitions to turn it into the 51st state of the USA.

A Conservative MP in Canada and a former ambassador were among those to criticise the UK prime minister for failing to stand up for their country.

The latest attack on Canada comes at a a difficult time for the Labour leader.

He is hoping to woo President Trump on a historic second state visit to the UK in September, when he will meet the King, a keen champion of the Commonwealth.

Liberal Democrat deputy leader Daisy Cooper said: “Once again, Donald Trump has shown contempt for his allies by continuing his damaging war on trade. With such an unreliable partner in the White House, the government needs to strengthen our economy, by establishing a bespoke UK-EU Customs Union, and work closer with our European and Commonwealth allies to create a coalition of the willing to end Trump’s trade war.”

SNP MP Stephen Gethins said: “The Trump project, just like Brexit, is about throwing up barriers to trade with our partners that will cost jobs and damage public finances. The UK needs to be building bridges with states like Canada and the EU that will help deliver sustainable economic growth. There have to be serious questions around the Labour government’s judgement over the offer of a state visit to Trump.”

The latest row erupted over Canada’s plans for a digital services tax.

In a post on Truth Social, the president complained that he had “just been informed” of the move, which could leave some American technology companies with large bills.

Trump called the plans “a direct and blatant attack on our Country.”

“They are obviously copying the European Union, which has done the same thing, and is currently under discussion with us, also,” he wrote, added that as a result the US was “hereby terminating ALL discussions on Trade with Canada, effective immediately.”

Trump later claimed the US has “a great relationship with the people of Canada” but that its government, headed by the former governor of the Bank of England Mark Carney, had made things “very difficult”.

He added: “We don’t want to do anything bad, but … economically … we have such power over Canada. I’d rather not use it, but they did something with our tech companies today, trying to copy Europe.”