LONDON (AP) — The Latest on President Barack Obama's visit to the United Kingdom (all times local):

2:00 p.m.

It's hard to make arriving via helicopter for lunch with the queen look like a casual affair, but Queen Elizabeth II nearly managed it.

Tying a scarf over her head, the queen and Prince Philip came out in light rain to meet President Barack Obama and first lady Michelle Obama as Marine One landed outside Windsor Castle.

After quick but warm greetings, the four got into a black Range Rover. Philip drove and Obama joined him in the front seat. Britain's longest-serving monarch sat in the back.

At the castle, the 90-year-old queen got out of the SUV largely by herself, nearly before Obama could assist. Inside, she could be heard noting almost apologetically that "this room is full of mirrors" and asking Obama where he'd like to sit.

The first lady's office says her magenta and black floral print dress was made by Oscar de la Renta. She wore a black, Narciso Rodriguez overcoat.

The queen wore a smart, blue suit and black, square-heel pumps. Her head scarf was a small, floral print.

1:20 p.m.

After dinner with two princes on Friday, President Barack Obama will dine with an ambassador and a prime minister the following day.

The White House says U.S. Ambassador Matthew Barzun will host Obama and British Prime Minister David Cameron for dinner Saturday at his London residence, Winfield House.

Set amid 12 acres (5 hectares) of grounds in London's Regent's Park, the 1930s neo-Georgian mansion is palatial. But it's not as historic as 300-year-old Kensington Palace. That's where the president and first lady Michelle Obama will dine Friday as guests of Prince William, his wife the Duchess of Cambridge and his younger brother Prince Harry.

1:00 p.m.

President Barack Obama has arrived in Windsor, England, for a royal lunch with Queen Elizabeth II.

The two heads of state were sitting down at Windsor Castle, just west of London, on Friday. It's the day after the queen and much of Britain celebrated her 90th birthday. First lady Michelle Obama and Prince Philip, the queen's husband, were joining the meal.

Obama says he'll wish the queen a happy birthday in person.

The queen and Prince Philip came out to greet Obama and the first lady in a light drizzling rain as they disembarked from Marine One at Windsor Castle.

Obama's socializing with the British royals was continuing later Friday over dinner with Prince William, his wife Kate and brother Prince Harry at Kensington Palace in London.

He was meeting with Prime Minister David Cameron in between the royal engagements.

9:00 a.m.

Campaigners for a British exit from the European Union are expressing anger at U.S. President Barack Obama's call for the U.K to stay in the bloc. U.K. Independence Party leader Nigel Farage says Obama should "butt out."

Obama due to meet Prime Minister David Cameron later Friday.

London Mayor Boris Johnson, a leader of the exit campaign, says Americans "would never contemplate anything like the EU for themselves." Writing in The Sun newspaper, Johnson said Obama's stance "is a breathtaking example of the principle of do as I say, not as I do."

8:50 a.m.

President Barack Obama is urging Britons to vote to stay in the European Union, saying the challenges in the world require allies to "stick together."

In an op-ed published in the Telegraph newspaper, Obama says Great Britain's presence in the EU "magnifies" Britain's influence and helps spread "British values."

The piece was published Thursday evening as Obama arrived in London for a three-day visit. Some have speculated that the trip is timed to boost the campaign against the so-called "Brexit" ahead of a June referendum. Not all Britons are welcoming Obama's opinion.

Obama writes he's offering his view "with the candour of a friend" and notes the decision will affect U.S. interests.

He writes, "The U.S. and the world need your outsized influence to continue - including within Europe."