The next day, Mr Trump and Ms May will visit an unspecified defense site before holding talks at Chequers, the prime minister's country retreat 65 kms from the capital.
The visit, which coincides with Theresa May's second anniversary as Prime Minister, is expected to be met by protests, including the flying of a blimp depicting the 45th president of the United States as an angry orange baby over London.
Most recently, the separation of migrant children and parents at the US-Mexico border reignited calls for May to call off Trump's visit.
The US government says President Donald Trump is set to make his first visit to Britain since taking office.
Mr Johnson denied that Mr Trump was avoiding London, where the biggest protests are expected to take place, pointing out that he was using the ambassador's residence in Regent's Park as his base for the visit, staying overnight there on Thursday, the day he arrives.
"They will be discussing that issue - the relationship with Russian Federation - at the meeting at Chequers", Mr. Johnson said, referring to the prime minister's ceremonial country estate in Ellesborough, about 45 miles northwest of London.
"We are a free and open democracy, and we believe in the right to peaceful protest".
The US President also sparked a backlash from author JK Rowling, among others, when he lashed out at Khan immediately after a London terror attack a year ago which killed seven people and left 48 injured.
Regardless, protesters seem to have grand plans for the US President's visit.
Trump's statement further irritated London, as many people and government officials asked May to withdraw her invitation to Trump to pay a state visit.
And while the president is conducting his meetings, the first lady, Melania, will have an agenda of her own, in the company of her opposite number, Philip.
Instead the president will be whisked off for a tour of some of England's most impressive historic buildings before departing for Scotland for a relaxing weekend, part of which is expected to be spent on the golf course.
Johnson said Trump's visit to Britain is meant to improve relations, and said trade between the countries has risen 21 percent since the start of the year.
"The president is simply trying to get as impactful a trip as he can get in a 24-hour period", Woody Johnson said.
President Trump will fly in to the United Kingdom on Thursday afternoon with First Lady Melania Trump, following a North Atlantic Treaty Organisation summit in Brussels.
The president can feel Churchillian at Blenheim Palace, where Winston Churchill was born.
They added that Trump Baby "can become a permanent feature of this terrible Presidency, a constant, unmissable reminder of the contempt with which this embarrassment of a man is held by everyone outside of his deranged, bigoted base".