Obama descends on Britain to try and persuade them NOT to leave the EU (oh, and he's going to meet the Queen)
Air Force One touched down at London Stansted shortly after 9.30pm
Obama waved as he walked off the plane following flight from Saudi Arabia
He will be joined by First Lady Michelle Obama for lunch with the Queen
President also seeks to use visit to show his support for staying in the EU
President Barack Obama has arrived in London for a three-day visit that will include dining with the royal family - and trying to keep Britain in the EU.
The president will use his visit to try and persuade British voters not to ditch their membership of the European Union (EU) ahead of a June 23 referendum.
The prospect of a British exit from the economic union is referred to as 'Brexit' in the UK and British Prime Minister David Cameron has specifically asked Obama to intervene in favor of staying in the EU.
He will be joined in London by First Lady Michelle Obama and they will have lunch Friday with Queen Elizabeth II - a day after her 90th birthday.
The pair will also attend a dinner hosted by Prince William, his wife, Kate, and Prince Harry at Kensington Palace.
Obama is expected to speak out in opposition of Britain's exit from the European Union as he meets with Cameron on Friday.
The United States has made it clear that they are opposed to Britain voting to leave the EU and Obama is expected to make a very rare political intervention in another country's domestic affairs.
His visit is a welcome one for Prime Minister David Cameron, who is leading the 'In' campaign.
However, it has drawn scorn from those arguing that Britain should leave the EU.
Obama is likely to suggest Britons should vote to stay in the bloc to preserve Britain's wealth, its 'special relationship' with the United States and the cohesion of the West.
Speaking prior to his arrival, Ben Rhodes, Obama's deputy national security adviser, said: 'As the president has said, we support a strong United Kingdom in the European Union.'
The US government - and many US banks and companies - fear a Brexit would unleash market turmoil, diminish British clout, undermine London's status as a global financial capital, cripple the EU and undermine Western security.
The president's intervention in the so-called 'Brexit' debate has already sparked criticism from some who say he is meddling in Britain's business.
Air Force One touched down at Stansted Airport shortly after 9.30pm on Thursday after visiting Saudi Arabia where Obama held talks with King Salman.
Upon arriving, the president waved as he exited the plane before being greeted on the tarmac.
He was then ushered into the presidential helicopter Marine One before being taken from the airport.
Police were seen increasing security in and around the airport throughout the day.
Armed officers were stationed around the terminal and outer fencing to ensure the president touchdown safely.