Barack Obama arrived in Britain on Thursday night with a forthright warning that the UK would be less able to deal with economic shocks, terrorism and the migration crisis if it leaves the EU.

The US president will use his three-day visit to urge British voters to embrace “the remarkable legacy” of the EU in building peace since the second world war, a message which has infuriated Brexit campaigners.

But Mr Obama will defend his right to speak out, saying that the US soldiers who died on the battlefields of Europe had demonstrated that America had a stake in the outcome of Britain’s EU referendum on June 23.

“The tens of thousands of Americans who rest in Europe’s cemeteries are a silent testament to just how intertwined our prosperity and security truly are,” he wrote in the Daily Telegraph.

“And the path you choose now will echo in the prospects of today’s Americans as well.”

His intervention is seen in Downing Street as a crucial moment in the referendum campaign. Mr Obama will reinforce his message in a press conference with David Cameron on Friday at Number 10.

The official reason for Mr Obama’s talks with Mr Cameron is to discuss the threat of Isis; the extension of economic sanctions against Russia over its aggression in Ukraine will also be discussed.

The security risks facing Europe provide a convenient backdrop for Mr Obama to make his claim that US/UK relations are best served by Britain being an active participant in its own continent.

The tens of thousands of Americans who rest in Europe’s cemeteries are a silent testament to just how intertwined our prosperity and security truly are. And the path you choose will echo in the prospects of today’s Americans as well

The Brexit campaign is divided on how to respond to Mr Obama’s intervention: some accuse him of interfering in domestic politics, while others fear that attacking the US president will simply look “nasty”.

Boris Johnson, London mayor, has taken the former approach, accusing Mr Obama of “hypocrisy” and arguing that the US would never share sovereignty with a supranational body like the EU.

Iain Duncan Smith, former work and pensions secretary, has claimed that Mr Cameron had gone down “on bended knee” to plead for Mr Obama to “bully” the British public into voting to stay in the EU. He said on Thursday: “I could imagine no circumstances under which he would lobby for the US Supreme Court to be bound by the judgments of a foreign court.”

Dominic Raab, the pro-Brexit justice minister, accused Mr Obama of “wanton double standards”, arguing that the US would never consider opening its border to free movement from Mexico or giving judges from Venezuela a say in US law.

Mr Raab told the BBC that Mr Obama was motivated by “selfish national interest” and wanted London to be Washington’s mouthpiece in Europe. He said that Britain’s interests did not always align with those of the US.

But one pro-Brexit minister said: “There will be 48 hours of positive headlines for the other side and we just have to accept that. Then, once Obama is gone, we can rejoin the battle.”

Sir Peter Westmacott, former British ambassador to Washington, said that Mr Obama was simply saying that the UK’s current relationship with the EU put it in “a very important place”.

Apart from the talks in Downing Street, Mr Obama will have lunch with the Queen at Windsor Castle on the day after the monarch’s 90th birthday.

The US president will also have dinner with Prince William, the Duchess of Cambridge and Prince Harry on Friday before holding a “town hall” meeting in London on Saturday.

Mr Obama will argue on his visit that EU membership “magnifies” British influence and helps it to shape global events, including dealing with terrorism, migration and economic shocks.

His references to US sacrifice on European soil in the second world war are a pre-emptive strike against those critics in the Leave camp who argue that the president has no business interfering in the referendum debate.