Two months before the UK votes on whether to stay in the European Union or leave, US President Barack Obama has warned that Britain would go to the "back of the queue" when it comes to trade deals if they do opt to exit.
"Let me be clear — ultimately this is something British voters have to decide for themselves," Obama said. "But part of our special relationship, part of being friends is to be honest and to let you know what I think."
Obama emphasized that his interest is selfish, saying it "affects our prospects as well... The US wants a strong UK as a partner, and UK is at its best when it's leading a strong Europe."
He continued: "I don't believe the EU modifies British influence, it magnifies it," and concluded: "I think there's a British poet who once said no man is an island, even an island as beautiful as this. We're stronger together."
Obama's comments were made during a joint press conference held by the US president and British Prime Minister David Cameron held in the ornate surroundings of the Foreign and Commonwealth Office (FCO's) Locarno room — the same place where the Locarno Treaties were signed in the mid-1920s to promote reconciliation in Europe after World War One.
The conference was in one sense a chance for the two to mark out what they claim to have achieved together during the six years they have both been in power, along with jokes about their "special relationship," compliments (Cameron called Obama "a man with a very good heart" who gives "sage advice"), and references to a game of table tennis which they both seemed to remember differently (Cameron said Obama beat him, Obama said they were both beaten by a pair of schoolchildren).
Obama arrived in the UK on Thursday evening for a three-day visit — his fifth as US president.
Earlier on Friday, Obama and his wife Michelle had lunch with Queen Elizabeth II and her husband the Duke of Edinburgh at Windsor Castle. The queen turned 90 on Thursday, and Obama said he wanted to wish her "a happy birthday in person."
The US president and Cameron held private talks before the conference, with 10 Downing Street rolling out a red carpet for Obama.
On Friday, Obama also published an op-ed in the Daily Telegraph where he referred to the "special relationship... forged as we spilt blood together on the battlefield" between the two countries and said he and Cameron would discuss the Islamic State (IS) and other political conflicts in the Middle East — including Yemen and Libya.
Polling company Ipsos Mori found the British public roughly split on whether Obama should or shouldn't be expressing a view on the referendum.
Writing in the Sun, London Mayor Boris Johnson — a leader in the campaign to leave the EU — called Obama "hypocritical."
"Much as I admire the United States, and much as I respect the President, I believe he must admit that his country would not dream of embroiling itself in anything of the kind," he wrote of EU membership. "The US guards its democracy with more hysterical jealousy than any other country on earth."
"For the United States to tell us in the UK that we must surrender control of so much of our democracy — it is a breathtaking example of the principle of do-as-I-say-but-not-as-I-do."
At Friday afternoon's press conference, Obama smiled when asked whether he was acting hypocritically by voicing his opinion on the referendum. "You shouldn't be afraid to hear an argument being made," he said.
Cameron responded too, saying: "as we make this choice it surely makes sense to listen to what our friends think."
The prime minister refused to air his views in the other direction though, after an American journalist asked him about the US presidential election.
"As a friend speaking honestly, what would you advise American voters to do about [US Presidential candidate] Donald Trump?" the journalist asked.
"I've made some comments [about the American elections] in recent months and I don't think now is a moment to add to them or subtract to them," Cameron replied, adding that as prime minister of Britain "you always look on at the US elections in awe at the scale of the process and the length of the process."
On Friday evening, Obama went on to have dinner with Prince William and his wife Catherine, along with William's younger brother Prince Harry.
Follow Sally Hayden on Twitter: @sallyhayd