President Trump has said he apologised to Britain's Prime Minister Theresa May over the interview with The Sun newspaper in which he praised her rival Boris Johnson and criticised her handling of the Brexit negotiations, saying her proposed solution would 'kill' any deal with the US.

His intervention could not have come at a worse time for May, who is struggling to control a party deeply divided over her strategy. Several senior members of the government including Johnson, formerly foreign secretary, and David Davis, formerly Brexit secretary, have already resigned in protest.

However, Trump said today that May was 'a total professional'. 'I said, "I want to apologise because I said such good things about you," And she said, 'Don't worry, it's only the press,' he claimed.

He said: 'Unfortunately, there was a story that was done which was generally fine but it didn't put in what I said about the prime minister and I said a tremendous thing,' he said. 'It's called fake news.'

He described the US-UK relationship as 'the highest level of special'. He added that he had made suggestions to May about Brexit rather than telling her what to do.

'As far as the advice, I did give her a suggestion – I wouldn't say advice – and I think she found it, maybe, too brutal. And I could see that,' Trump said. 'I gave her a suggestion, not advice. I wouldn't want to give her advice. I'd give her a suggestion.'

Speaking with the prime minister at a joint news conference, he said that 'whatever' the UK did after it left the EU was 'OK with me'.

May said they had discussed plans for an 'ambitious' trade agreement. 'We agreed today that as the UK leaves the European Union we will pursue an ambitious US-UK free trade agreement,' she said. 'The Chequers agreement reached last week provides the platform for Donald and me to pursue an ambitious deal that works for both countries right across our economies.'