LONDON (REUTERS, AFP) - Prime Minister Theresa May made a determined pitch to Donald Trump for a post-Brexit trade deal with the United States on his first trip to Britain on Thursday (July 12), just hours after the American president questioned her plans for leaving the European Union.

Invoking the spirit of Winston Churchill as she addressed Trump and business leaders at the British World War II leader's birthplace, May praised the friendship between the two close allies, glossing over remarks from the president that he was entering a "hot spot", with Britain in turmoil over Brexit.

Outside Blenheim Palace, near Oxford to the northwest of London, a couple of thousand demonstrators lined the road and booed before Trump's arrival, one of over 100 protests police expect to take place during his four-day trip.

After arriving by helicopter, Trump stood alongside May on a red carpet on the steps of Blenheim Palace while a military band of British army guardsmen, wearing tall black bearskin hats and red jackets, performed for the two leaders and their spouses.

Within the walls of the grand 18th-century mansion, May had only warm words, calling Britain and the United States "not just the closest of allies but the dearest of friends".

"Mr President, Sir Winston Churchill once said that 'to have the United States at our side was, to me, the greatest joy'," May was to tell Trump at a black-tie dinner in his honour, attended by senior ministers and about 100 executives from firms including Blackstone group, Blackrock, Diageo and McLaren.

"The spirit of friendship and co-operation between our countries, our leaders and our people, that most special of relationships, has a long and proud history. Now, for the benefit of all our people, let us work together to build a more prosperous future," she said in excerpts released in advance.

But in a series of extraordinary broadsides, Trump told Friday's edition of The Sun that May's plan for post-Brexit ties with the EU would "probably kill" the prospects for a trade deal with the US.

Trump also said former foreign minister Boris Johnson, who resigned this week in protest over the plan, would make "a great prime minister".

He said London mayor Sadiq Khan, who has allowed protesters to raise a giant diaper-clan balloon mocking the US president next to parliament on Friday, was doing "a terrible job" on crime.

The comments will plunge the transatlantic "special relationship" to new lows, making for extremely awkward talks with May when the two meet at her country retreat of Chequers later on Friday.

Trump's trip coincides with a tumultuous week for May after two senior ministers resigned in protest at her plans for trade with the EU after Britain leaves the bloc next March.

"I'm going to a pretty hot spot right now, right? With a lot of resignations," Trump, a major supporter of Brexit, told a news conference before leaving for London.

In his comments to The Sun, he said he had advised May to go about leaving the EU in a different way but was ignored.

"I would have done it much differently. I actually told Theresa May how to do it but she didn't agree, she didn't listen to me. She wanted to go a different route. "I would actually say that she probably went the opposite way. And that is fine. She should negotiate the best way she knows how. But it is too bad what is going on," he told the tabloid, Britain's best-selling newspaper.

Referring to the Brexit blueprint, which was outlined by the government on Thursday, he said: "The deal she is striking is a much different deal than the one the people voted on.

"It was not the deal that was in the referendum. I have just been hearing this over the last three days. I know they have had a lot of resignations. So a lot of people don't like it," he said.

May is facing a rebellion by Brexit hardliners over the proposals, including the resignation of Johnson and Brexit minister David Davis this week, although moderates and big businesses have been supportive.

May's "business-friendly" Brexit plan - which would keep Britain in a free trade zone for goods with the EU but mean it has to share some EU rules - was agreed by her cabinet only last Friday after two years of wrangling since Britons voted to leave the bloc in a 2016 referendum.

Some Brexit supporters cast it as a betrayal, including lawmakers in her own deeply-divided party who have warned of a leadership challenge.

"The people voted to break it up, so I imagine that's what they'll do. But maybe they're taking a little bit of a different route, so I don't know if that's what they voted for," said Trump.

Asked about Trump's comments, May simply said she was delivering wishes of the British people.

UNPRECEDENTED OPPORTUNITY

Trump, who has repeatedly praised Brexit, has expressed enthusiasm for a wide-ranging agreement with Britain after its EU departure. Supporters of Brexit say such a trade deal would be one of the great benefits of exiting the bloc.

In her Blenheim Palace address, May listed existing trade links, citing how more than a million American worked for British-owned firms and that Britain was the largest investor in the United States.

"Now, as we prepare to leave the European Union, we have an unprecedented opportunity to do more," she said.

Trump's victory in the 2016 presidential election shocked British diplomats in Washington and relations between May, a vicar's daughter, and the president have been strained at times.

Trump has frequently angered British politicians: May criticised him for retweeting a message by a member of a British far-right group late last year. The speaker of Britain's parliament has said Trump would not be welcome to address it. And last year Trump was critisied across the political spectrum for deriding London's mayor's response to an Islamist attack.

Critics of Brexit argue that Britain's hand has been so weakened by the imminent departure from the world's biggest trading block that May has no option but to temper any criticism of Trump so as not to jeopardise any future UK-US trade deal.

"We're shocked that Theresa May has rolled out the red carpet for him," said academic Emily Jones, 40, one of those protesting outside Blenheim Palace.

"I think it's a travesty of British values. How can we roll out the red carpet for someone who stands for everything we stand against?"

A YouGov poll on Wednesday showed 77 per cent had an unfavourable opinion of the president and just 50 per cent thought his visit should go ahead.

Nick Hurd, Britain's Policing Minister, said police expected more than 100 protests across the country, including two large demonstrations in London on Friday.

"I think they like me a lot in the UK," Trump said in Brussels. "I think they agree with me on immigration. I'm very strong on immigration."