Boris Johnson has blasted Donald Trump's claims a comprehensive free trade agreement between Britain and the US would be impossible to negotiate after the US President trashed his Brexit deal.

Mr Trump dropped the diplomatic hand grenade in an interview with his friend Nigel Farage on LBC last night as he also urged the Brexit Party and the Tories to form an 'unstoppable' general election pact.

The Prime Minister has insisted that his Brexit deal would open the door to a lucrative and wide-ranging free trade deal with the Trump administration when Britain leaves the EU.

But last night Mr Trump said it would be difficult to trade with the UK under Mr Johnson's Brexit deal, telling Mr Farage: 'To be honest with you... this deal... under certain aspects of the deal... you can't do it, 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.'