EU referendum: Boris Johnson blasts US' 'exorbitant hypocrisy' as Obama set to intervene

London Mayor Boris Johnson has launched a scathing attack on Washington's position that the UK should remain within the EU.

With President Barack Obama reportedly set to jet into the UK in the next month to convince the British public to vote to stay in the bloc in a historic June referendum, Johnson took a swipe at the US. The prominent Eurosceptic said: "Coming from Uncle Sam, it is a piece of outrageous and exorbitant hypocrisy."

A prominent "Leave" campaigner, Johnson has voiced criticism of Britain's EU membership due to frustrations over the "the loss of sovereignty" and "the expense and the bureaucracy and the uncontrolled immigration." The US has made no secret of its desire for the UK to stay part of the EU.

A Number 10 source said: "You wouldn't look stupid saying that [the President is going to tell British voters to stay in the EU]. It would be pretty shocking if he didn't ask voters to stay in the EU." The Leave camp is furious at the direct intervention by Obama, reports suggest.

Johnson is the most high profile senior Conservative to break ranks with Prime Minister David Cameron and campaign to leave. Writing in the Telegraph, he said: "There is no country in the world that defends its own sovereignty with such hysterical vigilance as the United States of America."

Johnson added: "To this day the Americans refuse to kneel to almost any kind of international jurisdiction. Alone of Western nations, the US declines to accept that its citizens can be subject to the rulings of the International Criminal Court in The Hague. They have not even signed up to the Convention on the Law of the Sea. Can you imagine the Americans submitting their democracy to the kind of regime that we have in the EU?"

Brexit campaigners are beginning to feel the pressure at the prospect of an impending and direct US intervention on the matter. An online petition to "prevent Obama from speaking in Westminster regarding the In/Out referendum" has gathered over 18,400 signatures.

Johnson has insisted that Britain is strong enough to go it alone. He has also suggested that the UK could secure a deal similar to Canada, which signed a free trade deal with the EU in 2014. It is expected to come into effect next year.

In his piece, Johnson blasts perceived double standards from the US. "Why is it essential for Britain to comply with a system that the Americans would themselves reject out of hand?" He wrote. "Is it not a blatant case of 'Do as I say, but not as I do?'"