Sir Lynton Crosby said there was still all to play for in the EU referendum

A string of opinion polls today showed voters are ignoring the hard hitting intervention of Barack Obama and support for Brexit has gone up.

In the latest poll, by ICM, the campaign to leave the EU was ahead 46 per cent to 44 per cent - with the poll showing a two point rise for Out.

A survey by ORB showed the In campaign was in front by five points but that the gap had closed markedly since last week.

Meanwhile, data produced by Sky News suggested 57 per cent of the public would not be influenced by the President's claims.

Mr Obama enraged Vote Leave supporters on Friday by claiming Britain would be sent to the 'back of the queue' for trade deals if it quit jthe EU.

The new polls came as Sir Lynton Crosby today warned the campaign to keep Britain in the EU risks becoming complacent about the referendum despite there still being a 'marathon' to polling day.

Sir Lynton, who guided David Cameron and the Conservatives to victory in the general election, said the Brexit battle was far from over despite poll leads for Remain and Barack Obama's noisy endorsement.

The Australian pollster said 20 per cent of the electorate remained unsure about how to vote on June 23 - meaning there was still all to play for.

The latest poll from ORB handed Remain a five point lead - indicating 51 per cent currently plan to vote In and 46 per cent committed to Out.

The gap was down from the previous ORB result, which showed a nine point Remain lead.

Analysing the results for the Daily Telegraph, which were drawn up during the US President's visit, Sir Lynton said: 'I wouldn't be hanging out the victory bunting just yet. The marathon has barely begun.

'Some will ask how can Leave show a marginal improvement when so many commentators said the Remain campaign had a great week, boosted by the American President's visit, and his rallying cry for Remain.

'However, the effect of the president's visit may not yet be felt in the numbers as sometimes it take a while for factors to wash through. Also, people may not take much notice of what an outsider has to say.'

He added: 'Among all voters, Remain has seen a two-point decline in support to 51 per cent while Leave has enjoyed a two point increase to 43 per cent.

'While suggesting a tightening in the race, these movements are within the margins of error and so we need another week to see if the question seems increasingly settled.

'With turnout taken into account, Remain captures 51 per cent of all definite voters, down one point since last week, and Leave attracts 46 per cent, an increase of three points.'

ICM analyst Jennifer Bottomley said: 'Following Barack Obama’s intervention in the EU debate last week, the Remain campaign will have hoped for a boost in public support.

'During his three-day visit to London, Obama warned that the UK would lose influence if it were to leave the EU, and suggested that it could take up to 10 years to negotiate new trade deals with the US.

'However, this week’s data does little to support this idea.'

The latest ORB survey revealed a five point lead for the Remain campaign - down from the previous poll by the firm which showed a nine point lead

The poll found 57 per cent of people remain convinced the In campaign will win the referendum on June 23 while only around one in five people expect a Brexit vote.

Sir Lynton added: 'This vast gap in expectation means that the Remain campaign is still largely at risk of voter complacency.

'Many of their supporters will expect to win the referendum and thus fail to recognise the significance of their own vote.'

Labour MP Frank Field today warned Jeremy Corbyn was not following his own beliefs on the EU

Sir Lynton said it was too soon to tell what impact Mr Obama's visit and enthusiastic endorsement of Mr Cameron's campaign would have.

The US President enraged Vote Leave campaigners with a warning Britain would be at the 'back of the queue' for a trade deal with America.

In other campaign developments today, Frank Field, one of a handful of Labour MPs backing Brexit, said Jeremy Corbyn's decision to support Remain could be the 'second longest suicide note' in the party's history after the infamous election manifesto of 1983.

'Since we had Tony Blair's mega election victory in 1997 we have lost 4.2 million voters. Many of those - maybe a million at the last election - went to Ukip,' Mr Field told the BBC Radio 4 Today programme.

'They went because they thought we had a leadership which didn't represent their views about the nature of the country they wished to live in, the country they were born in. I think therefore the question about borders, and control over borders, is crucial to this referendum vote.'

Mr Field said he believed Mr Corbyn - who had a long record of Euroscepticism - had only come out for Remain because he feared a challenge to his leadership if he declared for Leave.

'Every key vote that we've had on Europe since I've been in House of Commons and since Jeremy joined the House of Commons, we've actually been in the same lobby together, critical of Europe,' he said.

'The truth is there is no threat to Jeremy's leadership because there is no alternative candidate. Therefore if it was done for that reason, it was done for very poor political reasons.'