The event will begin with a military parade featuring the bands of the Scots, Irish and Welsh Guards in the spectacular Great Court.
On Queen Elizabeth, he said: "She is a tremendous woman".
"We are committed to dialogue, including of course with those we strongly disagree with and in government we would find a way to work with his administration while also standing up for our values". "It's also about giving a boost to those in America resisting his policies", said Daniel Jones, 26, who wore a red boiler suit and baseball cap emblazoned with "TRUMP BABYSITTER". "We must show Trump and the Tories that we can and we will defeat the politics of division".
She praised the friendship between the two allies, glossing over Trump's previous remarks that Britain was a "hot spot" in turmoil over Brexit.
"Maybe they're taking a little bit of a different route [on Brexit], so I don't know if that's what they voted for", he told a press conference after the North Atlantic Treaty Organisation summit in Brussels.
"I would have done it much differently", he told the Sun, which urged its readers to back Brexit before a referendum in June 2016.
Trump said he would be spending little time in London because of protests against him planned there, which an include a blimp made to look like an infant version of the president.
The couple are staying at Winfield House, the residence of the ambassador to the United States, and ancestral home of Winston Churchill. Scottish police, however, said that the balloon could not fly over the Turnberry golf club Trump owns on the west coast of the country.
"I like him a lot", he said.
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"He's fundamentally damaging the culture, the discourse, the rules, the laws", said Calah Singleton, a 28-year-old writer who turned out in London.
As Air Force One landed, activists unfurled an enormous banner across Vauxhall Bridge in central London-across from the new American embassy-which read, "Donald Trump: Human Rights Nightmare".
The president also renewed his war of words with Sadiq Khan, saying the London mayor has "done a very bad job on terrorism". The 20-foot high blimp depicts the U.S. leader as an angry infant wearing a nappy and clutching a mobile phone.
And President Trump drives a bulldozer through the government's central claims about their compromise - that the United Kingdom would be able to get decent trade deals with the wider world, while sticking to the European Union rules.
In another blow to May, Trump said her now ex-foreign secretary "would be a great prime minister".
Theresa May's White Paper was published on Thursday outlining Britain's plan for leaving the European Union.
Soon after she published her controversial Brexit White Paper which has divided MPs within her own Conservative Party, May sought to win over the U.S. president after the Britain exits from the European Union in 2019.
US President Donald Trump arrived Thursday in Britain, where he will find his own wall set up even as preparations for protests against his four-day visit are in full swing. Two years ago, Khan first crossed Trump's radar by criticizing his call for a ban on Muslim immigration to the US.
On Friday, he will hold talks with May expected to focus on Brexit and Russian Federation, at the prime minister's Chequers country residence followed by a press conference.
On Thursday night, hundreds of demonstrators chanted outside the US ambassador's residence where Trump was staying on the outskirts of London, providing a preview of the forceful protests expected on Friday.