US President Barack Obama flew into Britain to begin what is his fifth and likely final presidential visit to the kingdom
London (AFP) - US President Barack Obama was set to wade into the poisonous Brexit debate on Friday and become Queen Elizabeth II's first lunch guest after turning 90.
Obama flew into Britain late Thursday to begin what is his fifth and likely final presidential visit to the kingdom.
The president, along with First Lady Michelle Obama, will pay tribute to the queen, who celebrated her 90th birthday on Thursday, when they meet at Windsor Castle, west of London.
"The president has very much enjoyed his engagements with the queen over the years," said top Obama foreign policy aide Ben Rhodes.
The queen has reigned since 1952, during which time she has met with a string of US presidents from Harry Truman to Obama, who leaves office in January.
After lunch at Windsor Castle, Obama will travel to Prime Minister David Cameron's Downing Street office for talks that come ahead of a crunch British referendum on its European Union membership on June 23.
Obama is sure to be asked to weigh in on the controversial issue during a joint press conference afterwards, or at a town hall-style meeting with youngsters on Saturday.
Britain's departure from the EU -- a so-called Brexit -- could have deep ramifications for Washington's "special relationship" with London, and on the stability of the 28-country bloc itself.
Obama has consistently said he favours a strong Britain in a strong EU.
- Cameron stresses shared values -
Seen from Washington, Cameron's decision to call a referendum was a bold -- if not downright risky -- gamble that could leave Britain and the EU badly weakened.
"Obama is not an instinctive pro-European," said Ian Bond of the London-based Centre for European Reform think-tank.
"He opposes Brexit because it risks creating more problems for America in Europe."
Polls put the pro-EU and Brexit camps neck-and-neck among those who express a preference to vote.
Obama's "focus is on how Brexit would affect Europe's ability to help America tackle international problems," said Bond.
Britain has long been a key conduit for US influence in Europe.
Downing Street insisted that close ties would endure and sought to underscore areas of continued cooperation by saying the talks would focus heavily on the fight against the Islamic State jihadist group.
"Britain's relationship with the United States is special and enduring. Based on shared values and convictions it has stood the test of time," Cameron said.
"I am deeply proud of what it has allowed us to achieve, in dealing with the global challenges we both face and ensuring the security and prosperity of our people."
"I am confident that Britain and the US can continue to build on a solid basis of friendship and a shared commitment to freedom, democracy and enterprise to shape a better world for future generations."
- Brexit intervention risk -
Obama's seven years in office have seen the United States try to disentangle itself from wars in the Muslim world and pivot toward the growing economies of Asia.
But sovereign debt crises, jihadist terror attacks and now Britain's potential exit from the EU have thrust Europe back onto Obama's agenda.
However, for the US president, wading in is not without risk.
Pro-Brexit supporters have issued calls for the US president to stay out of the European Union referendum debate and cast him as a meddling outsider.
Nigel Farage, leader of the anti-EU UK Independence Party, said Obama should "butt out" while former cabinet minister Iain Duncan Smith said he failed to see how an intervention by the US leader could be "appropriate".
More than 100 members of Britain's parliament have reportedly written to the US ambassador in London to make their displeasure known.
It could be a potent argument in a country that shares cultural affinities with the United States, but which is deeply wary of being treated as Washington's lapdog.
During Obama's visit he and the first lady will also have dinner on Friday with Queen Elizabeth's grandson Prince William, his wife Kate and his brother Prince Harry.
From Britain he will travel to Germany for a meeting with German Chancellor Angela Merkel and other EU leaders.