His visit is a welcome one for Prime Minister David Cameron, leading the “In” campaign, but has drawn scorn from those arguing Britain should leave the EU.

Obama is likely to suggest Britons should vote to stay in the bloc to preserve Britain’s wealth, its “special relationship” with the United States and the cohesion of the West.

“As the president has said, we support a strong United Kingdom in the European Union,” Ben Rhodes, Obama’s deputy national security adviser, told reporters in Washington ahead of the trip.

After a visit to Saudi Arabia, including talks with King Salman, Obama flies to London on Thursday evening.

The U.S. government—and many U.S. banks and companies—fear a “Brexit” would unleash market turmoil, torpedo British clout, undermine London’s status as a global financial capital, cripple the EU and undermine Western security.

Polls on Wednesday showed British voters leaning towards the “In” camp, but many remain undecided.

Asked about Obama’s views, Cameron told the British parliament:

“Personally I believe we should listen to advice from friends and other countries and I struggle to find the leader of any friendly country who thinks we should leave.”

Cameron has said that in the face of what he terms Russian President Vladimir Putin’s aggression, this is no time to drop out of the club Britain joined in 1973.

“Butt Out”

“The UK economy will be better off within the Union than if it leaves,” Charles Kupchan, the senior White House director for European affairs, said ahead of the trip. “And as a key economic partner, that’s an issue of interest to the United States.”

Opponents of the EU—many of whom laud the U.S. alliance—say 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.

New York-born Boris Johnson, the London mayor who heads the “Out” campaign, said he did not want to be lectured by Americans about EU membership.

“President Obama should butt out,” Nigel Farage, another prominent opponent of EU membership, told Reuters in an emailed statement.

“This is an unwelcome interference from the most anti-British American president there has ever been. Mercifully, he won’t be in office for much longer.”

“Out” campaigners have said the United States would never agree to dilute its own national sovereignty in the way the EU requires of its member states.

Obama’s term in office ends next Jan. 20. On Friday he will have lunch at Windsor Castle with Queen Elizabeth, who celebrates her 90th birthday on Thursday, and her husband Prince Philip.

After lunch, Obama will hold talks with Cameron followed by a briefing with reporters and dinner with Prince William, his wife Kate and Prince Harry at Kensington Palace.

Obama, who will be joined by his wife Michelle in London, will hold a discussion meeting with young people on Saturday before departing for Germany.