Jeremy Corbyn, criticised by some for offering only lukewarm backing for his party's "In" stance, will tell supporters today that remaining in the EU would protect jobs, pitching to Labour voters who campaigners say will be key in deciding the outcome of the June 23 referendum.

The vote will help determine Britain's future in trade and world affairs but also shape the EU. The pound and euro have lost value on fears a British exit from Europe, or Brexit, would tip the 28-member bloc back into recession.

With Prime Minister David Cameron's Conservative Party deeply split over the issue, the prime minister, who wants to keep Britain in the EU, has recently given the left-leaning opposition party the lead role in the "Remain" campaign.

According to a YouGov poll for yesterday's Times newspaper, the "Out" campaign has opened up a 7-point lead over "In" while an ORB poll for The Daily Telegraph put "Out" one point ahead.

In another, though not unexpected, boost for the "Leave" campaign, media tycoon Rupert Murdoch's Sun newspaper called on its readers to vote to quit the EU.

"The Sun urges everyone to vote Leave. We must set ourselves free from dictatorial Brussels," said the tabloid, which has a circulation of 1.7 million but may be preaching to the converted as many of its readers already back a Brexit according to polls.

Bookmakers, which up until last week had the "In" camp as firm favourite, have been slashing the odds on Brexit.

"We were forced to shorten our Brexit odds yet again overnight ... and the momentum is such that it seems inevitable Brexit will be favourite by the weekend if this trend continues," said Graham Sharpe, William Hill's spokesman.

The uncertainty around the result has led to huge swings in the value of sterling. On Tuesday, it was down almost 1 percent against the dollar and half a percent against the euro compared to closing levels in New York but was holding just above two-month lows hit on Monday.

RELYING ON LABOUR

Polls suggest a majority of Conservative voters back Brexit, which means Cameron is relying on Labour, which is much more pro-EU, to help win the vote to stay in the bloc.

Labour's leftist leader Corbyn, who says the EU is not sufficiently just but that his party has decided it is best to campaign for justice within the bloc, has been accused of not doing enough so far to galvanise its supporters. He denies the charge.

A YouGov poll late last month showed nearly half of Labour supporters did not know the party backed staying in the EU.

A YouGov poll late last month showed nearly half of Labour supporters did not know the party backed staying in the EU

Corbyn will join with his senior team and trade union leaders on Tuesday to make what he will describe as "Labour's case" to remain.

"Today I am issuing a call to the whole Labour movement, to persuade people to back Remain to protect jobs and rights at work," he will say, according to advance extracts of his speech.

"We have just nine days to go to convince Labour supporters to vote Remain."

Tuesday's event, part of what the "In" camp has dubbed the "Labour fight-back", follows a speech by former Labour prime minister Gordon Brown on Monday in which he said Britain should be "leading not leaving" the bloc.

While those wanting to stay in the EU can count on the support of many of Britain's biggest businesses, most economists and foreign leaders such as U.S. President Barack Obama, fears about uncontrolled immigration from Europe and the impact on jobs and services is proving key for the "Out" campaign.

"If we stay in the EU, as Cameron wants, we will finally give up any chance of controlling our population," The Sun tabloid said in its front-page editorial.

Associate Editor Trevor Kavanagh told BBC radio on Tuesday it was the paper's editor who had made the decision to back Brexit rather than Murdoch, a longstanding and vocal EU critic, although in March Kavanagh had said it would be Murdoch who would decide.

"We can only say what we believe, and I think that a lot of our readers do believe what we say, not because we say it but because they've come to that conclusion themselves," Kavanagh said.

In an article for the London Evening Standard in February, veteran journalist Anthony Hilton said he once asked Murdoch why he was so opposed to the European Union.

"'That's easy,' he replied. 'When I go into Downing Street they do what I say; when I go to Brussels they take no notice'."

At a 2012 public inquiry into the press, Murdoch rejected suggestions he had influence over British politicians.

In a world of declining sales and burgeoning new and social media, the stance taken by the press is viewed as mattering less than it once did.

"I think the British public don't always take the press stories with the seriousness that perhaps journalists think they do," Oliver Daddow, a Senior Lecturer in International Relations at Nottingham Trent University, told Reuters.