article: Mr Obama, who is on a three-day visit with his wife Michelle, is meeting PM David Cameron for talks. Mr Obama has told the Daily Telegraph being in the EU magnified Britain's influence across the world. But London Mayor Boris Johnson called his view "hypocritical", describing the EU system as "alien" to US traditions. Prime Minister David Cameron is hosting Mr Obama at Downing Street. The leaders are holding talks on the fight against so-called Islamic State (IS) and will later be joined by the UK's home, foreign and defence secretaries, and the chancellor. Mr Cameron and Mr Obama are expected to discuss the progress being made in combating IS in Iraq and what more can be done to tackle the group in Syria. The situation in Libya, where the West is considering how to support the newly-established Government of National Accord (GNA) in the battle against IS, will also be discussed. The pair will later hold a joint press conference. Earlier the president and First Lady Michelle Obama attended a private lunch with the Queen and Duke of Edinburgh at Windsor Castle - the day after the Queen's 90th birthday celebrations. The Obamas brought the Queen a photo album of her many visits with US presidents and first ladies. The album begins with her visit to the United States in 1951. Then known as Princess Elizabeth, Duchess of Edinburgh, she toured George Washington's Mount Vernon Estate and met with President Harry Truman at the White House. The Duke and Duchess of Cambridge and Prince Harry will welcome the Obamas for dinner at Kensington Palace on Friday evening. BBC deputy royal correspondent Sarah Campbell The Duke of Edinburgh drove the Queen into the Castle grounds to meet the president and first lady as they disembarked from their helicopter. After a quick chat, there was some discussion over where people should sit, with Mr Obama opting for the front seat. Prince Philip, aged 94, returned to the wheel. This is the third time the couples have met and the first time in the historic surrounds of Windsor Castle. Their last meeting was during a visit in 2011 when the Obamas stayed in Buckingham Palace. In 2009, in what was taken to be a sign of a friendly relationship between the families, the first lady was photographed with her arm around the Queen's waist. In their meetings since, including today, there does seem to be a genuine warmth between the two families. Today's lunch is private. To the frustration of the many journalists covering this visit, whatever the Queen makes of the president's views on Britain in Europe will remain within the castle walls. The president's intervention in the UK's forthcoming EU referendum on 23 June has been hotly debated and sparked claims of "hypocrisy" from those who want to leave the EU. They claim the US "would never contemplate anything like the EU for itself". In an article for the newspaper, President Obama acknowledged that ultimately the matter was for British voters to decide for themselves. But he also said: "The outcome of
summary: Barack Obama has urged the UK to stick with the EU, as he began his final trip to Britain as US president by having lunch with the Queen.