As Sir Keir Starmer prepares to meet Donald Trump for key talks in the White House, observers will be looking for signs of the health or otherwise of the “special relationship” between the UK and the US.
Here the PA news agency takes a look at previous relationships between prime ministers and presidents, and the key challenges they faced.
– Winston Churchill and Franklin D Roosevelt
The so-called “special relationship” between the UK and US shaped interactions between prime ministers and presidents as it developed throughout the 20th century.
It was Winston Churchill who coined the phrase during a speech in Missouri in 1946.
The fact that Mr Churchill was invited to stay at the White House during a trip to Washington following the Japanese attack on Pearl Harbour in 1941, which forced the Americans directly into the war, was seen as a reflection of how close the transatlantic alliance had become.
But an anecdote from the time suggests the relationship went beyond conventional diplomatic boundaries.
One morning, then-president Franklin D Roosevelt was said to have entered Mr Churchill’s suite to find the prime minister emerge “pink, glowing and completely naked” from the bath.
As an embarrassed president turned to leave, Mr Churchill said: “The prime minister of Great Britain has nothing to conceal from the president of the United States.”
The two men later that year signed the Atlantic Charter, a key joint declaration outlining a broad statement of British and US war aims.
– Howard Macmillan and John F Kennedy
Howard Macmillan and Dwight D Eisenhower developed a positive relationship during the Second World War when the former was a Cabinet minister and the latter a supreme allied commander in the Mediterranean.
In 1959, Mr Eisenhower accepted an invitation from the then prime minister to London – the first state visit by a US president in half a century.
But perhaps more significant was the visit of Mr Eisenhower’s successor John F Kennedy in June 1961, which followed a meeting between the young president and Soviet leader Nikita Khrushchev in Vienna.
John F Kennedy visited the UK in 1961 (Alamy/PA)
The meeting during the height of the Cold War was described as “bruising”.
With Mr Kennedy suffering from acute back pain, Mr MacMillan discarded plans for a big meeting with advisers in favour of a private chat in his room, which featured sandwiches and whisky.
Mr Kennedy was said to have “unburdened himself” about the Vienna meeting, later describing the meeting as a “special moment”.
– Jim Callaghan and Jimmy Carter
Labour prime minister Jim Callaghan worked hard to cultivate a positive relationship with newly elected Jimmy Carter in 1977.
Mr Callaghan is said to have significantly developed Mr Carter’s understanding of European affairs and also sought to improve his difficult relationship with German leader Helmut Schmidt.
A trip to Tyneside featured in the US president’s visit to Britain in May 1977.
– Margaret Thatcher and Ronald Reagan
The relationship between Margaret Thatcher and Ronald Reagan is often singled out as a high point in US-UK relations, but interactions between the two were not always cordial.
Mr Reagan gave special addresses to both Houses of Parliament in June 1982, only one of three US presidents to do so since then.
Ronald Reagan with Margaret Thatcher in London (PA)
However, later Mrs Thatcher remarked that their relationship “worked… because he was more afraid of me than I was of him”, while there are accounts of ferocious rows over issues such as the Falklands conflict, the US invasion of Grenada in 1983, and Mr Reagan’s “Star Wars” defence project.
But mutual respect is said to have been maintained throughout these exchanges, with both passionate defenders of the transatlantic alliance and a shared vision seen as playing a key role in ending the Cold War.
– Tony Blair and George W Bush
The connection shared by Tony Blair and George W Bush has proved hugely controversial.
Mr Blair formed a strong political alliance with Mr Bush on foreign policy with a backdrop of the emergence al Qaida.
In a post-9/11 speech Mr Bush said that “America has no truer friend than Great Britain”, but the close relationship between the two was frowned upon by some in the Labour Party and members of the public uncomfortable with US influence and a perception that the relationship was not equal.
Mr Blair continued to argue that it was in Britain’s interest to “protect and strengthen the bond” with the US regardless of who is in the White House.
The prime minister in 2003 signed the “The letter of the eight” supporting US policy on Iraq and built his foreign policy on the principles of close ties with the US and the European Union.
Tony Blair welcomes American President George W Bush to the first meeting of the G8 Summit in 2015 (PA)
But the strategy included an interventionist streak which led to Britain joining the US in the global “war on terror”.
This led the UK to participation in the 2002 invasion of Afghanistan and the invasion of Iraq in 2003.
The Iraq war attracted widespread public criticism in the UK and beyond, while 139 Labour MPs opposed it.
The circumstances of the decision on the UK’s participation were intensely scrutinised, with claims that Iraq leader Saddam Hussein controlled weapons of mass destruction later proved to be false.
As casualties in the war mounted, Mr Blair was accused of misleading Parliament and his popularity dropped.
However, he did win a third term but some would argue his domestic achievements have been overshadowed by his support for Mr Bush and their shared approach to Iraq.
– David Cameron and Barack Obama
During David Cameron’s term in office, Barack Obama addressed Parliament in another demonstration of the importance of the special relationship to both countries.
However, in 2016 Mr Obama partly blamed European leaders for the chaotic state of Libya following the fall of Colonel Gaddafi.
He accused Mr Cameron of being “distracted by a range of other things” and said he had “more faith in the Europeans”.
Barack Obama with David Cameron (PA)
In an interview published in The Atlantic, Mr Obama touched on an issue that is set to be a key feature of Sir Keir’s talks with Donald Trump when he lamented “free riders” in the international community and seemed to suggest Britain was in danger of falling into that category.
According to the article, the US president told Mr Cameron at a G7 summit in Bavaria in 2015 that “you have to pay your fair share” on defence spending if the special relationship is to continue.
Soon after, Downing Street announced that the UK would meet a Nato commitment to spend 2% of gross domestic product on defence.
– Theresa May and Donald Trump
Theresa May arrived at the White House just a few days after Donald Trump’s first inauguration in 2017, in what was seen as strong sign that positive relations would endure.
Ms May was reportedly focused on persuading Mr Trump to make a supportive statement about Nato, amid concerns he was too sympathetic to Vladimir Putin.
But it was pictures of the President holding Ms May’s hand as they walked through the White House that dominated coverage across the world.
Donald Trump walks with Prime Minister Theresa May prior to a joint press conference at Chequers in 2018 (Stefan Rousseau/PA)
Mr Trump’s first term is perceived as a time of relatively chaotic foreign policy, while reported comments at the time suggest the president did not see Ms May as “strong”.
What followed was the US unilaterally withdrawing from the Iranian nuclear treaty and the Paris climate accord among other unpredictable moves.
During a visit to the UK in 2018, Mr Trump said the relationship between the two countries was “very, very strong” but he was highly critical of Ms May’s approach to negotiations with the European Union over Brexit.
Despite this element of friction, the pair again held hands ahead of a press conference at Chequers.