(Bloomberg) - President Barack Obama said Britain would be at "the back of the queue" to negotiate a trade agreement with the US if it votes to leave the European Union, in a direct assault on the arguments of those who say the UK could win better deals outside the bloc.
"Some of the folks on the other side have been ascribing to the United States certain actions we will take if the UK does leave the EU," Obama said at a joint press conference in London on Friday (April 22) with Prime Minister David Cameron.
"For example, that, well, we'll just cut our own trade deals with the US. Maybe at some point down the line there might be a UK-US trade agreement, but it's not going to happen anytime soon."
The intervention is a boost to Cameron as he fights to keep Britain inside the 28-nation EU, with the use of the British word "queue" rather than the more American "line" suggesting the White House may have coordinated on the language.
The emphasis on trading isolation closed a week that began with a warning from the UK Treasury that a so-called Brexit would cause decades of economic damage.
While campaigners to get Britain out of the EU had begun the week arguing that the words of a foreign leader would make no difference to British voters, their reaction by Friday suggested concern.
London Mayor Boris Johnson wrote in The Sun newspaper that Obama's intervention was "downright hypocritical." He suggested the "part-Kenyan" president might dislike Britain's imperial legacy.
The point was taken up by Nigel Farage, leader of the UK Independence Party, which advocates Brexit. "Look, I know his family's background," Farage told the Guardian.
"Kenya. Colonialism. There is clearly something going on there. It's just that you know people emerge from colonialism with different views of the British. Some thought that they were really rather benign and rather good, and others saw them as foreign invaders. Obama's family come from that second school of thought and it hasn't quite left him yet."
Obama rejected that idea. "We are so bound together that nothing's going to impact the emotional and cultural affinities between our two countries," he said.
The president had opened with a long statement setting out all the advantages of keeping Britain inside the EU. "Part of our special relationship, part of being honest is to let you know what I think," he said, as he discussed the June 23 referendum.
"Speaking honestly, the outcome of that decision is a matter of deep interest to the US. It affects our prospects as well."
He said international cooperation through institutions such as the EU was good for security and the global economy, even if that came at the cost of giving up a little sovereignty. "I'm not coming here to fix any votes, I'm offering my opinion," he said.
The president met Cameron after a lunch with Queen Elizabeth II and before dinner with Prince William and the Duchess of Cambridge, during a visit sandwiched between a summit of Persian Gulf countries in Saudi Arabia and an international trade fair in Germany.
According to Joe Twyman, head of political polling at YouGov Plc, Obama's words on their own will make little difference. Their effect will be as part of a series of warnings that Cameron will issue in the weeks before the vote.
"He still has heft but the individual impact of events like this on public opinion is minimal," Twyman said. "Instead, it is the cumulative impact over weeks and months that is important."
Changing Minds A Pew Research Center poll in June found that 76 per cent of Britons have confidence in Obama on matters relating to world affairs, and the polling company Ipsos Mori on Friday said that 15 per cent of Britons say his view on the referendum is important to them in deciding how they'll vote.
"President Obama may not change the minds of many leave supporters - indeed they want him to stay out of the debate," said Gideon Skinner, head of political research at the pollster.
"But he could play a bigger role in bolstering the views of those already leaning towards Remain."
The Ipsos Mori data show the British public is split over whether Obama should express his opinion on the referendum, with 49 per cent saying he should and 46 per cent saying he shouldn't.
Separately, the bookmaker Ladbrokes Plc on Friday said that 90 per cent of all bets taken in the past two days have been for "Remain." The prospects of a "Leave" vote fell to 29 per cent from 34 per cent, it said. The Bloomberg Brexit Tracker puts the probability of vote to quit the EU at about 20 per cent.
For Cameron, the president's words needed little comment. "This is our choice, nobody else's," he said. "As we make that choice, it surely makes sense to listen to what our friends think."