The queen has received more than 100 heads of state since succeeding her father on the throne, in 1952. The list includes royals such as King Abdullah of Saudi Arabia, former dictators such as Nicolae Ceausescu of Romania and presidents like Michael D. Higgins, the first Irish head of state to travel on a state visit to London.
"We took Nicolas Sarkozy to the United Kingdom for a state visit less than a year after he became president of France, and that was unusual." Mr. Westmacott said. "It was not because the UK wanted anything in particular from it, it was rather that France is our closest and most important neighbor, and we would normally try to get a state visit for such an important figure in the paper as soon as possible."
"State visits are quite personal," he added. , "And often it happens that the sooner you organize one, the greater the impact it has"
But only two American presidents have been in Britain on a state visit: George W. Bush, in 2003; and Barack Obama, in 2011. As part of a triumphant tour of Europe in 1961, President John F. Kennedy traveled to London, but was not granted the pomp of a state visit. Mr. Kennedy and his wife, Jacqueline, had a private dinner with the queen.
"The reason why we often do not get a full-fledged state visit by a president of the United States, I think, is that it's four days, and it's often difficult for the leader of the free world to spend so much time outside in one country, "said Westmacott.
Some British plan to protest in the streets
The announcement of Mr. Trump's visit received mixed reactions from British politicians and the public. British Foreign Secretary Boris Johnson used Trump's erratically capitalized tweet format to convey his enthusiasm for welcoming the American president:
"Hoping to see our closest friend and ally at the GREAT visit "he wrote on Twitter.
Nigel Evans, a conservative member of Parliament, also hailed the visit, calling it "excellent news" that will strengthen the relationship between Britain and the United States.
The mayor of London, Sadiq Khan warned that the US president could face protests if he visited the capital.
Politicians and anti-Trump activists across Britain are mobilizing online to organize mass protests during Mr Trump's planned visit. A Facebook event for the protest has already gathered more than 100,000 supporters.
"When Donald Trump arrives on these shores, we and thousands of our supporters will make our voices heard," Kate Allen, Amnesty International UK. director, he said in an interview with BBC Radio Kent.
Some of Trump's critics have said that the president canceled a previous work visit scheduled for early this year because of his concern over the protests. At that time, Trump said he canceled the trip, originally planned for the opening of the new US Embassy, because he considered the relocation of the building a "bad deal" under the Obama administration.
What about Britain?
Mrs. Mayo was the first foreign leader to visit the White House after Trump took office. For the British Prime Minister, relations with Washington are particularly important given that Britain is scheduled to leave the European Union next year.
Mrs. You can expect to reach a free trade agreement with the United States once you leave the Europe-free trade area.
Apart from commercial interests, the British take pride in their "special relationship" with Washington, and British officials see their country as the closest security and intelligence partner in the United States.
But after having promoted the idea of a state visit for Mr. Trump, Ms. May has put that idea on ice in the face of widespread public and political opposition. The online petitions against the visit received hundreds of thousands of signatures and provoked a lively debate in Parliament, in which the character of Mr. Trump and his aptitude as a guest of the state were discussed.
Mrs. Meanwhile, May had to watch as French President Emmanuel Macron forged unexpectedly warm ties with Mr. Trump.
So Mr. Trump's visit to Britain provides an opportunity for Ms. May to show that she has maintained a close relationship with the president, despite recent tensions.
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