US president Barack Obama lunches with Queen Elizabeth on Friday at Windsor Castle and meets prime minister David Cameron, but the focus on his visit to Britain will be on how strongly – and publicly – he voices his opposition to a so-called "Brexit. "
The president and his officials have made no secret that Mr Obama is not in favour of one of the closest allies to the United States leaving the European Union should the British people so decide in a referendum on June 23rd.
The White House is of the view that the United Kingdom is better off from a political and economic perspective within the 28-member bloc.
Mr Obama tends to be careful not to intervene in sensitive domestic political matters on foreign visits but his staff have signalled that the president may be inclined to speak out on this subject if the topic is raised.
“We have no closer friend in the world and if we are asked our view as a friend, we will offer it,” Ben Rhodes, Mr Obama’s deputy national security adviser, told reporters last week in a preview of his four-day visit.
“But he’ll make very clear that this is a matter that the British people themselves will decide when they head to the polls in June.”
Should he voice an opinion at least privately, the US president would not be alone in chipping in his tuppence worth from a foreign audience.
The International Monetary Fund, a Washington-based guardian of global economic order, warned last week that a British exit from the EU could cause "severe regional and global damage", disrupt established trading relationships and cause "major challenges" for the UK and the rest of Europe.
On Wednesday, a day before Mr Obama's arrival in London on Thursday night, eight former Democratic and Republican treasury secretaries urged Britain to stay in the EU, warning in a letter published in the London Times that leaving would be "a risky bet on the country's economic future".
“A strong Britain, inside the European Union, remains the best hope in our view for securing Britain’s future, creating a more prosperous Europe and protecting a healthy and resilient global economy,” they said.
The letter was signed by Mr Obama's first-term treasury secretary Timothy Geithner, as well as Hank Paulson, John Snow, Paul O'Neill, Larry Summers, Robert Rudin, Michael Blumenthal and George Schultz, who served during President Richard Nixon's tenure.
Mr Obama stepped into the “Brexit” debate last July, telling the BBC that having Britain in the EU gave the US “greater confidence about the strength of the transatlantic union and is part of the cornerstone of institutions built after World War Two that has made the world safer and more prosperous”.
London mayor Boris Johnson, one of the senior Tories to break ranks with Mr Cameron and push for an EU exit, accused Mr Obama of "outrageous and exorbitant hypocrisy," saying that the US defended its own sovereignty with "hysterical vigilance" and would never tolerate the EU's restrictions.
White House spokesman Josh Earnest, in response, said last week that Mr Johnson had "a well-established reputation for rhetorical flourishes".
The White House has expressed concern about the effect of Britain’s departure from the EU club on the efforts to tackle migration and terrorism.
"We would not want to see a Brexit that could potentially damage the European Union and increase the challenges that it faces," Charlie Kupchan, Obama's senior director for European affairs, said.
The Transatlantic Trade and Investment Partnership, the EU-US trade deal on Mr Obama’s economic agenda in his final year in office, figures prominently too in the president’s “pros” column for the UK staying put.
Taoiseach Enda Kenny made the Irish opposition to “Brexit” known to Mr Obama during their St Patrick’s Day meeting. Mr Kenny said afterwards that the US president was “interested in the challenges that prime minister Cameron faces internally and externally” in his campaign to stay in the EU.
The US president is expected to talk about those challenges directly when he takes questions from reporters at a joint press conference with Mr Cameron at 10 Downing Street before he and first lady Michelle Obama dine with Prince Charles, the Duchess of Cambridge and Prince Harry at Kensington Palace.
