Labour must not sit out EU battle in hope of Cameron defeat, says Ed Miliband

Labour voters must not sit out the European referendum battle because they hope for a humiliating defeat for David Cameron but should instead campaign for a Remain win, Ed Miliband said.

The former Labour leader, in his first major speech since quitting after the general election defeat, acknowledged some of the party's voters felt "ambivalent" about the June 23 vote and had concerns about the impact of European Union immigration.

But he stressed that Brexit would "irreparably" set back Labour's cause and lead to the creation of an "offshore" Britain with cuts to regulation and workers' rights.

In a speech in London, he told Labour voters: "We can't sit this one out. We can't sit it out because the choice is so fundamental in trying to build the kind of country we want. We can't sit it out when we know the decision of Labour voters will be so crucial to the outcome of this referendum."

The Opposition must not let the fallout from Iain Duncan Smith's resignation overshadow the campaign to remain in the EU, he added.

"The civil war in the Conservative Party - IDS versus George Osborne, all of that stuff - cannot be allowed to obscure the central question in this referendum, which is: Are we more likely to secure social justice and progressive change inside or outside the EU? My answer is resoundingly that we should vote Remain."

He added: "We can't think 'well this is David Cameron's referendum, let's leave it to him and see what happens and won't it be embarrassing to him if he loses' because it's just far more important to Britain than any individual politician."

Jeremy Corbyn, who has in the past expressed doubts about the values of EU membership, has been accused by critics of playing too low key a role in the Remain campaign.

Mr Miliband said his successor will enter the fray with a speech after the Easter break, with fellow ex-leader Gordon Brown also being lined up to play a central part.

But he acknowledged that "Labour voters want information about where Labour stands" on the issue.

The former Labour leader said the Leave campaign had an agenda for a "more unequal, unfair, unjust Britain" with cuts to regulation and workers' rights.

He highlighted the views of Boris Johnson, Nigel Farage and Mr Duncan Smith, claiming they were united in seeking a "free market, low-regulated, race-to-the-bottom offshore Britain".

But he acknowledged there were concerns among Labour supporters about the EU, including the prospect of the Transatlantic Trade and Investment Partnership (Ttip) deal with the United States.

"Some people on the Left look at what has happened in the European Union in recent years and see quite a lot they don't like: they don't like austerity, the remoteness of some EU institutions, the response to the migration crisis, the proposed trade agreement with the US.

"Some Labour voters worry about free movement of workers and in particular what it means for them."

But Mr Miliband said it was a "fantasy" to think the problems of the 21st century could be solved by acting alone outside the EU.

He stressed that the impacts of EU migrants coming to the UK and potentially undercutting the wages of British workers could be limited if the UK Government acted.

"The workers brought in and used to try and undercut wages, the loopholes in rules which seem to mean unfair treatment, the exploitation of migrant workers to undermine terms and conditions - this is a profound issue," he said.

"But the answer is not to leave the European Union."

A vote to leave could still result in the UK being subject to free movement rules, as Norway is, he added.

"The real answer is to do a far better job of tackling exploitation here at home. Exploitation that this Government chooses not to act on."

Former home secretary Alan Johnson, who is leading the Labour In campaign, warned that Brexit could trigger the break-up of the UK.

"I think it's a very real threat," he said. "If I was a Scot and they voted overwhelmingly to remain in the EU and the rest of the country voted to leave - I think this might be an issue in Wales to a lesser degree as well - that would be the catalyst for another referendum."

He called for "prominent Labour figures" to intervene in the debate and acknowledged that it was "fair enough" to question Mr Corbyn's commitment to the EU when he was first elected leader but stressed that he was now "wholeheartedly committed to remain".