President Donald Trump is said to have given a "positive" and "complimentary" speech about England as he addressed US Embassy workers within hours of his arrival in the UK.
He touched down in Britain for his first official visit and has already brushed off mass protests by saying: "I think they like me a lot in the UK" and caused Theresa May a major new headache over Brexit.
Most people, a number of whom said they worked at the embassy in London, were tight-lipped as they left a secured area in the park near the US ambassador's residence, where Trump and his wife Melania will stay overnight.
Some cited "job restrictions" while another said he was wary of the press. But one woman said Trump had given a "short speech" which she described as "lovely".
Another man, who did not wish to give his name, said: "It was very complimentary to England and to the allies that we have, very positive."
The US President, 72, who will meet the Prime Minister and Queen during a four-day red carpet visit, landed at Stansted Airport on Air Force One at just before 2pm (UK time) and walked off hand-in-hand with First Lady Melania.
America's Commander-in-Chief has 1,000 of his own staff in the UK and a giant motorcade led by his bomb-proof Cadillac nicknamed "The Beast" as well as multiple helicopters including Marine One to fly him around.
The President and his First Lady were met on the tarmac by US Ambassador Woody Johnson and UK Trade Secretary Liam Fox before he was whisked off to Johnson's house near Regent's Park.
Late afternoon, Trump was seen with Melania departing for Blenheim Palace ahead of a gala dinner with US and UK business leaders.
He was pictured getting into Marine One in a tuxedo with the First Lady, who was wearing a floor-length, pleated buttercup yellow gown.
The magnificent English country house, which was built in the early 18th century, was the ancestral seat of Sir Winston Churchill, who was born there in 1874.
President Trump was greeted by PM May when he arrived at the UNESCO World Heritage Site, which is in Oxfordshire.
He is expected to be given a tour of Blenheim's grounds by the 12th Duke of Marlborough, Jamie Blandford - also known as Jamie Spencer-Churchill.
Blandford has had a much-publicised struggle with drug addiction - a habit he gave up a decade ago - and has previously been jailed after run-ins with the law.
Last year, he confessed: "I changed religion when I went to jail. I became a Muslim because you got more food. It wasn't the time of Ramadan. I luckily hit it just right – just afterwards!"
Following his tour, Trump will be joined by his wife Melania at a black tie dinner of about 150 business chiefs.
Melania was wearing a J Mendel SS18 gown costing £5000 ($9750).
Guests are expected to enjoy a meal of Scottish salmon, English beef and a desert of strawberries and cream.
As part of the exclusive event, business figures from dozens of FTSE100 firms will have the chance to hear from the Donald as he speaks about his industrial and trading policies.
Among those on the guest list are British Petroleum chief executive Bob Dudley, the European boss of Goldman Sachs, Richard Gnodde, and Facebook UK and Ireland boss Steve Hatch.
There were a number of protesters outside Blenheim Palace demonstrating against the presence of the American president in the UK.
Trump is believed to be a great admirer of Churchill's, having last year demanded that a bust of the wartime leader be returned to the White House after President Obama removed it.
Churchill was a descendant of Sir John Churchill, for whom Blenheim Palace was built in reward for his successes during the War of the Spanish Succession.
'A lot of people like me there'
Earlier, Trump gave an extraordinary press conference in Brussels after giving NATO leaders a bruising over defence cash, where he wrote off protesters and said Theresa May's Brexit deal probably wasn't what Britons voted for.
When asked about the threat of mass demonstrations he said: "I think it's fine. A lot of people like me there. I think they agree with me on immigration. I think that's why Brexit happened."
Protesters have pledged to follow him wherever he goes in Britain and 10,000 police officers have been drafted in to protect him - the largest number deployed since the 2011 riots.
Almost two million people signed a petition demanding he be banned from the UK because they believe he is sexist and racist and "Stop Trump" campaigners say he will face a "Wall of Sound" outside all the landmarks he visits because supporters will bang pots and pans.
Despite not being an official state visit, the Government is desperate to ensure the US leader feels he is being treated with the appropriate level of pomp and ceremony.
He will be treated to a Guard of Honour when he meets the Queen at Windsor Castle for tea tomorrow, there will also be a grand dinner at Blenheim Palace tonight as well as a lunch with Theresa May at Chequers on Friday (UK time).
Friday night he will stay at the US Ambassador official residence in Regent's Park, London, which has been surrounded by a ring of steel of new security fences and road barriers to prevent a terror attack.
On Saturday he will fly up to Scotland to play golf at one of his resorts and his son Eric landed in the family's "Trump Force One" private jet at Aberdeen, before flying to Helsinki to meet Vladimir Putin on Monday.
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.
And he made clear that he did not approve of the softer stance the PM has been advocating despite fury from many Tory MPs.
"Brexit is Brexit, the people voted to break it up so I would imagine that is what they'll do, but they might take a different route, I'm not sure that's what people voted for," Trump said, adding: "They're great people - I just want them to be happy. The EU better be careful. I warned them. Immigration is taking over Europe."
He added it seemed as if the UK was "getting at least partially involved back with the European Union".
"I'd like to see them be able to work it out so it could go quickly," he said.
Protests will culminate in a 70,000-strong march through London from Portland Place to Trafalgar Square.
The "Stop Trump" march is part of a wider "carnival of resistance" across the UK while he is here.
Other protests - including several "family friendly" gatherings - will take place at every place he will visit over the coming days.
Today Metropolitan Police Commissioner Cressida Dick declared: "We will keep him safe."
The Metropolitan Police will be responsible for the protection and security of the US president and will also try to ensure lawful protests can be staged.
Dick said: "We will keep him safe. We will facilitate lawful protest and we will uphold other people's rights as much as we can."
She was speaking at the Air Power Conference in London where 450 guests included RAF personnel, foreign air chiefs, academics and industry specialists.
Dick said: "Later today we have a visiting head of state from across the pond.
"Tomorrow we have some large protests in central London and as the president of the United States makes his way through the country it is the Metropolitan Police who are responsible for his protection and security.
"Tonight there will be protests, tomorrow there will be protests.
"On Saturday there will be sort-of related protests (from the) far-right and far-left and probably the most difficult."
Command suites and coordinating groups based in Lambeth, south London, will involve a wide range of people including from all the emergency services, the military, Foreign Office and Home Office, plus officials who run transport services in London and beyond.
Dick said they will be linked through to units at the same level in sectors such as the intelligence world.
She added: "They will be talking to teams on the ground and they will be liaising with police services up and down the country. They will be doing that in concert with the Civil Aviation Authority, the US Air Force and the RAF.
"We in this country, and I hope I do not regret saying this, are very good at this sort of thing."
Dick also said the workforce which is having to "flex, surge and to respond" to events is made up of "fantastic people with a clear sense of mission, high skills and amazing ethics".
The capital's Mayor Sadiq Khan has allowed a group to fly a giant balloon showing Trump as a baby in a nappy over the capital during his visit.
Nearly every force in England and Wales has contributed officers to help with the massive mobilisation, the biggest since the 2011 riots.
The US President arrives after giving NATO leaders a tongue-lashing in Brussels over defence spending and controversial comments about Britain being in "turmoil".
He said he got along with Theresa May "very well", but suggested he might make time during his UK visit to speak with his friend Boris Johnson, who has just rocked her Government by resigning as foreign secretary.
It was "up to the people" whether or not they want May to stay as Prime Minister, he added.
The tight security surrounding the visit will attempt to avoid exposing Trump to planned protests in central London.
His schedule involves a black tie dinner at Blenheim Palace with US and UK business leaders and cabinet ministers, hosted by May.
Ahead of his arrival the PM said she would use the visit to "forge a strengthened, ambitious and future-proof trade partnership" with the US after Brexit.
May said there is "no stronger alliance" than the special relationship between the two countries and "there will be no alliance more important in the years ahead".