5 things you should know about President Obama's visit to the UK

Why is he here?

He is in London for a three-day visit to “allow the President to offer his gratitude to the British Government” and give thanks for U.K. support throughout his presidency, an official statement said.

He then heads to Germany to meet with Chancellor Angela Merkel and visit Hannover Messe, the world’s largest trade show for industrial technology.

A White House official confirmed that Mr Obama and Mr Cameron will attend a private dinner hosted by US ambassador Matthew Barzun at his official residence Winfield House in Regent’s Park on Saturday.

Who else is he meeting?

This lunchtime he met with the Queen and Prince Philip alongside his wife Michelle after landing in the grounds of Windsor Castle in his Marine One aircraft. This afternoon he is meeting with Prime Minister David Cameron and will also have dinner this evening with Duke and Duchess of Cambridge and Prince Harry at Kensington Palace.

What will he say?

Today in a press conference he is going to make a strong case for Britain to stick with the EU at the June 23 referendum. He hinted at much of this in an opinion piece he write in the Telegraph newspaper.

He wrote: “The United States sees how your powerful voice in Europe ensures that Europe takes a strong stance in the world, and keeps the EU open, outward looking, and closely linked to its allies on the other side of the Atlantic. So the US and the world need your outsized influence to continue - including within Europe.”

He will also talk about the importance of working with Britain to combat so-called Islamic State.

Why does he care so much about the EU?

He claims it is to do with a shared sense of history between the US and UK.

“I will say, with the candour of a friend, that the outcome of your decision is a matter of deep interest to the United States,” he said.

“The tens of thousands of Americans who rest in Europe’s cemeteries are a silent testament to just how intertwined our prosperity and security truly are. And the path you choose now will echo in the prospects of today’s generation of Americans as well.”

Why have some kicked up a fuss about Obama’s intervention?

Those campaigning to leave the EU think that the President has over stepped the mark by intervening on an issue that is not related to US politics.

“It’s a breathtaking example of the principle of do-as-I-say-but-not-as-I-do,” Brexiter Boris Johnson wrote in The Sun newspaper. He believes that America would never enter into an EU style agreement which gives up sovereignty to neighbouring countries of Canada and Mexico.

Ukip defence spokesman and MEP for Yorkshire and the Humber, Mike Hookem, said: “To use the sacrifice of those who gave their lives in the fight against a foreign power who had a desire to rule Europe somehow seems sick.

He added: “Mr Obama’s interference in our democracy is unwanted.”