Donald Trump Theresa May
File photo: Tensions are rising between Trump and May. Christopher Furlong/Getty Images

Future trade relations between the United States and the post-Brexit United Kingdom are under threat due to President Donald Trump's anger towards Prime Minister Theresa May.

The two leaders' relationship reportedly "soured" and Trump has pulled out of plans to visit the UK. The two formed a strong relationship a week after Trump's inauguration but a response from May to one of the President's tweets could now prove costly.

May publicly criticised Trump for retweeting anti-Muslim videos posted by anti-immigrant group, Britain First. According to the Sunday Times, a source revealed: "His position is that if Britain is not interested in me, then I am not interested in them."

Foreign Secretary Boris Johnson, writing in a column for The Telegraph, said the UK should be rolling out the welcome mat for Trump. He said Labour was risking "damaging the national interest" by opposing a visit from Trump.

"In 2016, the people of the United States not only elected Donald Trump; they bought £100 billion of British goods and services," Johnson wrote. "That is more than twice what we sold Germany - our second biggest export market."

"So when the Labour party rails against "Donald Trump's America" they might remember that those same freedom-loving Americans bought 200,000 British cars, including 114,000 Jaguar Land Rovers - helping to sustain 40,000 jobs in those superb factories in the West Midlands."

May is hoping to smooth things over with Trump at the Swiss summit this week, but might face an uphill battle.

A different source revealed to the Sunday Times that: "A trade deal with the US might be number one on the UK's list but it's not top of his list of priorities."

Trump allies say the crux of his problems with the UK surrounds the dossier put together by former MI6 officer Christopher Steele, not the Twitter storm. Those documents allege Trump conspired with Russia during his election campaign.

"Trump is fuming with capital letters," the source revealed. "The British involvement in what he sees were efforts to discredit him during the presidential campaign have infuriated him."