Boris Johnson's Brexit plan would prevent the United Kingdom and United States from striking a trade deal, Donald Trump has said, in an intervention which threatens to damage the prime minister's nascent election campaign, Eurasia Diary reports citing Business Insider.

Speaking to Brexit Party leader Nigel Farage on LBC Radio on Thursday evening, the US president said: "To be honest with you, this deal, under certain aspects of the deal, you can't do it. You can't trade.

"We can't make a trade deal with the UK because I think we can do many times the numbers that we're doing right now and certainly much bigger numbers than you are doing under the European Union."

Trump added that the terms of the deal struck between the UK and EU meant that "under certain ways, we're precluded," adding that it was "completely ridiculous."

Under the terms of Johnson's agreement with the EU, the UK will leave the customs union, meaning it will be free to strike its own trade deal with countries around the world once it has left the bloc.

However, the UK government has said the country will maintain high standards in areas like food hygiene and animal welfare after Brexit, which has been interpreted as a potential impediment to a comprehensive deal with the US.

The prime minister has consistently talked up the prospect of a post-Brexit trade deal with the US as one of the biggest prizes of leaving the EU.

A Downing Street spokesman said afterwards: "'Under this new deal the whole of the UK will leave the EU Customs Union, which means we can strike our own free trade deals around the world from which every part of the UK will benefit."