President Obama and First Lady Land in London for G20 Summit

The presidential jet touched down just before 8pm and Mr Obama and his wife Michelle were greeted by Chancellor Alaistair Darling.

Mr Obama has scheduled a series of hectic series of discussions and summits with Nato, the G20 and a host of world leaders in private meetings across five countries.

The President was due to be carried by helicopter to the heavily guarded US ambassador's residence in Regent's Park.

He will hold a meeting with Gordon Brown tomorrow morning before the pair hold a joint press conference at the Foreign Office. Those discussions will kick-start a frantic 48 hours in London designed to culminate in a joint policy announcement from the G20 leaders.

On Friday and Saturday, Mr Obama will attend a Nato summit marking his first test abroad as US Commander-in-Chief and his best chance to sell his new plan for the Afghan war to wary allies.

After just two months in the Oval Office, the new US president is expected to try to leverage the Nato summit in Strasbourg, France, and Kehl, Germany, to build closer ties with America's defence allies. He will also hold meetings in the Czech Republic and Turkey.

The trip also marks the debut on the global stage of Michelle Obama, who also has a packed agenda of meetings and planned appearances. She will accompany the President when he meets the Queen at Buckingham Palace tomorrow.

Mr Obama's schedule includes bi-lateral meetings on the sidelines of the G20 with the leaders of Russia and China among others.

He will attempt to rebuild relationships with allied countries that split with Washington over the war in Iraq and subsequent treatment of prisoners.

The President's first meeting with Dmitry Medvedev, the Russian President, is expected to help thaw relations which suffered during Bush and Putin era.

President Medvedev wrote an editorial for the Washington Post today expressing his desire for a better relationship.

"Long ago, Alexis de Tocqueville predicted a great future for our two nations," Medvedev wrote. "So far, each country has tried to prove the truth of those words to itself and the world by acting on its own. I firmly believe that at this turn of history, we should work together."