Ignoring all diplomatic niceties, the convention-shredding USA president set up the four-day visit with a rebuke of his beleaguered host as she battles to stop her government falling apart over Brexit.
The Trumps arrived at Stansted Airport near London on Air Force One earlier that afternoon for the controversial trip to Britain.
Mrs May told the audience that the United States and UK are not just the closest of allies but "the dearest of friends".
Mr Trump with meet with UK Prime Minister Theresa May and the Queen. Yet no matter how much the president strives, he will still be the arriviste - desperate to be taken seriously by a clan that is not without its own share of scandals and misbehavior. "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.
Trump was flying over after a fraught North Atlantic Treaty Organisation summit in Brussels where he piled pressure on allies to double their defence spending. Some plan to stage an "all-night noise protest" outside the barricades surrounding Winfield House later Thursday, with those attending urged to "bring pots, drums and vuvuzelas".
The US President described Britain as a "pretty hot spot right now with a lot of resignations" and suggested his meeting with Vladimir Putin in Helsinki on Monday could be easier. Mr. Trump has been a keen supporter of Brexit and on Thursday he appeared to echo those concerns.
Trump's trip coincides with a tumultuous week for May after two senior ministers resigned in protest at her plans for trade with the European Union after Britain leaves next March.
"I don't know if that is what they voted for".
U.S. Ambassador Woody Johnson said Wednesday that citizens are often advised to avoid public demonstrations and that he is not upset by the decision to allow the "Trump baby" balloon to be displayed near Parliament.
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While Trump was critical of May, he was full of praise for Johnson, who he called "a very talented guy".
The convention-shredding president had ignored diplomatic niceties ahead of touching down for the four-day visit - his first to Britain since taking power - by rebuking his beleaguered host as she struggles over Brexit. The UK's speaker of parliament made clear that Trump, because of his values, would not be invited to address MPs.
After shaking hands, the Trumps and Mays turned to take in the scene.
"Donald Trump could do perfectly fine doing rallies in the USA".
"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.
The President, who is set for a two-day working visit followed by a weekend in Scotland, addressed the planned protests in a news conference, saying, "I think it's fine".
A YouGov/ITV Tonight poll released on Thursday found there is "broad support" for Trump among Britons.
In the busy south London neighborhood of Brixton, Victor Greetham, who runs a jazz bar, said he hasn't been to a demonstration since he protested against the Iraq War in 2003, but he planned to attend one of the protests against Trump's visit.
The dinner is Trump's official welcome to the United Kingdom during their first visit since Trump's election.