Photo by Carl Court/Getty Images
Obama is in the UK to help celebrate the 90th birthday of Queen Elizabeth II, as well as to hold talks with prime minister David Cameron, but he has also used his time to present the USA's position on the EU referendum, coming out heavily in favour of Britain staying in the 28-nation bloc.
Speaking at a press conference in Downing Street on Friday afternoon, Obama said he "wants Britain's influence to grow - including within Europe".
He continued to say that: "The UK is at its best when it's helping to lead a strong European Union. It leverages UK power to be part of the EU.
"I don't think the EU moderates British influence in the world, it magnifies it."
Those comments have angered campaigners for a so-called Brexit - Britain leaving the European Union. Liam Fox, the former defence secretary, and one of the most fierce aggregates of Brexit within the Conservative Party, called Obama's comments about the EU debate "largely irrelevant" on the BBC's Newsnight, on Friday.
"We heard 'you are our best friend, we have a special relationship, and you will get a punishment beating if you leave the EU'. This is very much the Downing Street refrain," Fox said.
Fox was not the only one to criticise Obama however, with another eurosceptic Tory MP, Dominic Raab, calling Obama a "lame-duck American president doing an old British friend a political favour" according to the BBC.
UKIP leader Nigel Farage also weighed in, accusing Obama of doing David Cameron's "bidding" calling his actions "shameful." Farage added that he though Obama is "talking down Britain."
Obama was criticised even before he'd spoken, following the publication of a column in the Daily Telegraph on Friday morning, where the president set out his pro-EU stance for Britain. This stance angered several prominent Brexiteers, including London mayor, Boris Johnson.
After giving his views on the Brexit debate, Obama and the first lady Michelle, moved on to have dinner with the Duke and Duchess of Cambridge at Kensington Palace, where they had the chance to meet Prince George for the first time.
On Saturday, Obama will meet with Labour party leader Jeremy Corbyn, and help mark celebrations for the 400th anniversary of William Shakespeare's death by visiting London's Globe theatre.