A new poll suggests US President Barack Obama's transatlantic visit to call on Britain to vote 'No' to a Brexit was a failure.

ICM Research has found that 46% of people now want the UK to exit the European Union, as the Leave campaign takes a narrow lead over those 44% in favour of staying.

Not only did Obama's impassioned call for a united Europe fail to bring about a Remain campaign rally, it seems to have had an adverse effect.

ICM has seen a hardening of resolve among Leave supporters when it comes to turnout on June 23rd, with four in five saying they will definitely vote.

This 80% figure is an increase over the 75% who said the same in IBM's first April survey, with the pollsters suggesting it reflects "a sense of displeasure among Leave supporters about Obama’s comments".

Meanwhile, just 65% of potential Remain voters say they are absolutely certain to vote, down 2% from early April.

In a Daily Telegraph column, Mr Obama had written that Britain would possible have a decade-long wait for a free-trade deal with the US if a Brexit was to come to pass.

Leading 'Vote Leave' figures took umbrage with the perceived pressure Obama was putting on British voters.

Boris Johnson, London's mayor and an anti-EU campaigner, wrote in the same publication that it would be wrong of Remain campaigners to "think they have bombed us into submission".

Ukip leader Nigel Farage told Sky News:

"If a British prime minister was to intervene in a presidential election, America would go absolutely berserk and say this was ridiculous outside interference. I’d rather he said nothing".