President Obama has arrived in the UK for the start of a four-day visit. Here is what he is expected to be doing today.

The Queen and Duke of Edinburgh will host a private lunch for the US President and his wife Michelle at Windsor Castle.

It is a post-birthday affair for the Queen, who turned 90 yesterday, so the Obamas are expected to come bearing a gift.

The couple struck up a firm friendship with the Queen when they came over for a state visit in 2011 and Michelle was even pictured with her arm around the Her Majesty's waist.

President Obama is also in the UK on business but joked: "I confess, I do want to wish Her Majesty a happy birthday in person."

After the lunch, Obama is expected to hold bilateral talks with David Cameron in Downing Street.

During his visit it is thought the President will try and persuade Britain to stay in the EU.

Writing in the Daily Telegraph, he said being part of the European Union "enhances Britain's global leadership".

He highlighted the special relationship between the US and the UK "forged as we spilled blood together on the battlefield, and added: "It is a matter of deep interest to the United States. "The path you choose now will echo in the prospects of today's generation of Americans as well."

The Duke and Duchess of Cambridge and Prince Harry have invited the Obamas to have dinner with them at Kensington Palace in the evening.

The Obamas met William and Kate during their 2011 state visit to the UK - less than a month after the royal wedding.

Last year, Michelle presented Prince George and Princess Charlotte with gifts - a rocking chair and personalised blanket for Charlotte and a children's wagon toy for George.

Prince Harry is also close to the Obamas having struck up a close friendship with the First Lady in particular through his support of wounded military personnel.