Obama, who opinion polls show is popular in Britain, applauded Britain’s EU membership which he said had helped make the world freer, richer and better able to tackle everything from migration to terrorism.
Invoking the interlinked history of the United States and Britain and the tens of thousands of Americans lying in European war graves, Obama implored voters to weigh the benefits of membership ahead of a June 23 referendum.
“The European Union doesn’t moderate British influence – it magnifies it,” Obama wrote in The Daily Telegraph, a eurosceptic British newspaper.
“As your friend, I tell you that the EU makes Britain even greater,” the headline of Obama’s article read.
His remarks, which led television news broadcasts in Britain, undercut one of the most passionate arguments of the opponents of EU membership: that Britain could prosper on an equal basis with global powers such as the United States.
A spokeswoman for Prime Minister David Cameron welcomed Obama’s intervention, but the president’s comments drew scorn from opponents of Britain’s EU membership.
New York-born London Mayor Boris Johnson, a leader of the “Out” campaign who hints he wants Cameron’s job, derided Obama’s arguments in a newspaper column that referred to “the part-Kenyan President’s ancestral dislike of the British empire”.
John McDonnell, the opposition Labour Party’s finance policy chief, called Johnson’s remarks “dog-whistle racism”.
The White House declined to comment and a spokesman for Johnson did not respond to requests for comment.
Obama said Britain’s closest ally wanted it to remain in the club it joined in 1973 to bolster trade and strengthen the 28-member bloc, which Washington views as a pillar of stability in the post-World War Two era.
The U.S. government, and many U.S. banks and companies, fear a Brexit would cause market turmoil, diminish the clout of Washington’s strongest European ally, hurt London’s global financial hub status, cripple the EU and weaken Western security.
“Now is a time for friends and allies to stick together,” Obama said. “Together, the United States, the United Kingdom, and the European Union have turned centuries of war in Europe into decades of peace, and worked as one to make this world a safer, better place.”
Opinion polls indicate that British voters are leaning towards the “In” camp but many remain undecided.
Younger voters are more likely to support remaining in the EU, but “In” campaigners are worried that older voters may be more likely to turn out to vote.
Before talks with Cameron in Downing Street, Obama and his wife Michelle congratulated Queen Elizabeth, who celebrated her 90th birthday on Thursday.
Prince Philip, Elizabeth’s 94-year-old husband, took the wheel of a Range Rover to drive the Obamas to lunch on the territory of Windsor Castle, a royal residence that traces its history back over almost 1,000 years to William the Conqueror.
Two years ago, ahead of a Scottish vote on independence, Obama said he hoped Britain “remains strong, robust and united”, a comment that was welcomed by unionist politicians in London. Scots voted to remain part of the United Kingdom.
Citing President Franklin D. Roosevelt’s 1939 toast to Washington’s close alliance with Britain, Obama lauded Britain’s contribution to the development of democracy, the rule of law and open markets.
“The U.S. and the world need your outsized influence to continue — including within Europe,” Obama said.
Opponents of the EU have said that membership has shackled Britain to the corpse of a failed German-dominated experiment in European integration, and that Britain, if freed, could prosper as a sole trader. Many of them are also supporters of a close relationship with the United States.
Such opponents caution that while many world leaders like Obama, banks such as Goldman Sachs and big companies such Ford may want Britain to remain in the EU, the British people do not appreciate being lectured about how to vote.
Nigel Farage, a prominent opponent of membership as leader of Britain’s UK Independence Party, called Obama the most anti-British American president to date.
“This is an unwelcome interference … Mercifully, he won’t be in office for much longer,” Farage said.