He landed at Stansted Airport Thursday afternoon and was whisked by helicopter to Winfield House, the American diplomatic residence in London.
His comments are a departure from his remarks earlier in the day when he insisted, "I think they like me a lot in the U.K" although he still insisted even after his Baby blimp lament that real Brits "love the President".
"I think he has done a bad job on crime, if you look, all of the terrible things going on there, with all of the crime that is being brought in".
I am just saying I think he would be a great Prime Minister.
"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".
On Thursday, CBS News' Haley Joelle Ott reports protesters numbering in the dozens showed up to express their outrage over the Trump administration's recently policy about separating children from their families at the border.
"We had an opportunity to have an exchange about economic developments, on issues such as migration, and also the future of our trade relations", she said, after a tete-a-tete on Trump's anti-EU trade war.
The Scotland United Against Trump group said it hoped about 3,000 people would gather for the protest, which will be held from 17:00 until about 21:00.
Thai Cave Rescue: Sixth Boy Leaves, Six Soccer Players and Coach Remain
Crowds at the teeming rescue site cheer the good news, but attention soon turns to the hard task of getting the boys out safely. Nargonsak said this phase may take longer than the previous two rescue missions, which both lasted several hours.
Protests began in London Thursday, as President Trump arrived for a quick "working visit" in Britain.
A protest was expected to take place near Blenheim Palace in Oxfordshire, the venue for President Trump " s black-tie dinner with Theresa May.
Trump said he would try to avoid the crowd in the capital during his four-day visit to the country.
May's government is trying to satisfy Britons who voted for their country to leave the bloc, but to set an independent course without hobbling businesses, security agencies and other sectors that are closely entwined with the EU.
But she also warned Trump not to ignore the "malign behaviour" of Moscow when he meets Russian President Vladimir Putin in Helsinki next week.
Mr Trump and his wife Melania arrived at Stansted airport, where he was met by the UK's global trade secretary Liam Fox.
About 150 guests are understood to have agreed to attend the dinner at Blenheim Palace, including cabinet members and business leaders.
The pair will then travel to Chequers - the PM's country residence in Buckinghamshire - for talks with the foreign secretary. Scottish police, however, said that the balloon could not fly over the Turnberry golf club Trump owns on the west coast of the country. This part of the visit is being considered private.
"What's clear is that anyone overnight who has been arrested by the police would be put in accommodation far superior to what the officers are staying in".