Of Johnson, he said: "I have a lot of respect for Boris".
While he stressed he did not want to get involved in the UK's internal affairs, he added: "The people voted to break it up so I would imagine that's what they would do, but maybe they're taking a different route". He added, "I think he is a great representative for your country".
A large police presence has been building up outside the palace in Oxfordshire and BBC News correspondent Duncan Kennedy said about 500-600 protesters bearing placards were demonstrating before Mr Trump's arrival.
"I guess when they put out blimps to make me feel unwelcome, no reason for me to go to London", Trump said.
Despite not being an official state visit, the Government is desperate to ensure the U.S. leader feels he is being treated with the appropriate level of pomp and ceremony. He is scheduled to have tea with Queen Elizabeth at Windsor Castle where her grandson Prince Harry married US actress Meghan Markle in May.
The state visit has never been scheduled - there is fierce opposition to it in many quarters of Britain - and this trip is part of a working visit instead, meaning, among other things, that Trump will overnight at Winfield House, the US ambassador's handsome residence near Regents Park rather than in Buckingham Palace or Windsor Castle as a guest of the queen.
He is due to leave on Sunday for talks in Helsinki the following day with Russian President Vladimir Putin, whose government May has accused of unleashing a lethal nerve agent in the city of Salisbury.
And he made clear that he did not approve of the softer stance the PM has been advocating despite fury from many Tory MPs.
U.S. President Donald Trump (R) speaks to Britain's Prime Minister Theresa May during in a working dinner meeting at the North Atlantic Treaty Organisation headquarters during a North Atlantic Treaty Organisation summit of heads of state and government in Brussels, Belgium, May 25, 2017. The EU better be careful.
The extra security measures may strike Londoners as incongruous, set amid the leafy surrounds of Regent's Park, a spot popular with joggers, picnickers and families.
The "Stop Trump" march is part of a wider "carnival of resistance" across the United Kingdom while he is here. 'You go through certain areas that didn't exist ten or 15 years ago.' He added: 'Allowing the immigration to take place in Europe is a shame'.
In Windsor, Berkshire, President Trump will receive the honour of an audience with the Queen and other members of the Royal Family.
Dick said: "We will keep him safe".
"He might not like the current president, but I represent the United States".
"Tonight there will be protests, tomorrow there will be protests". This protest is not anti-American-far from it.
The poll conducted this week said 63 percent found Trump racist, and 74 percent said he was sexist. "The fact that something so blatantly mocking and disrespectful to the most powerful man in the world would be permitted to fly in the air whilst he is visiting a foreign country speaks legions to her about how her husband's presidency is viewed internationally".