Labour leader Ed Milband played down a leaked document telling party activists to “move the conversation on” from immigration as he said he would make it a criminal offence for employers to undercut pay and conditions by exploiting migrant workers.

In the second of what Labour said were five key pledges for next year’s general election, Mr Miliband said the move would form part of a package to deal with concerns over immigration, also including the introduction of “proper” entry and exit checks, a limit on in-work benefits for EU migrants, and the extension to two years of the period before which immigrants can claim out-of-work benefits.

The pledge came as a leaked document showed that Labour activists had been urged by party chiefs to “move the conversation on” when voters raise the issue of immigration.

The paper, setting out plans to counter the challenge from Ukip, was sent to dozens of MPs in constituencies where the eurosceptic party threatens to rob the opposition of the votes needed to return to power at next May’s general election, the Daily Telegraph said.

At the end of his speech on immigration in Great Yarmouth, Norfolk, Mr Miliband described the document as “not very well drafted” but said there could be no suggestion he was seeking to dodge the issue.

He said: “I think what matters about our party is what I’m saying on this stage – the pledge we’re making rather than some not very well drafted language in a briefing document.

“I don’t think anybody’s in any doubt where Labour stands on this.”

He had not made any reference to the document during more than an hour of questions from the public but was pressed by journalists.

” We’re very clear about this, that’s why I’m standing on this stage with our pledge on immigration,” he said.

“The Labour Party not only takes this seriously, but I’ve changed Labour’s approach

“It’s the second pledge we’re making. It’s going to be on all our pledge cards for the general election.

“We think it is an important issue and it’s an issue we’re not only going to talk about but show the action we’re going to take.”

During his speech, Mr Miliband insisted: ” When people worry about the real impact immigration has, this Labour Party will always respond to those concerns, not dismiss them.

“It isn’t prejudiced to worry about immigration, it is understandable.”

And he said that leaving the EU, as Ukip advocates, would be “a disaster for jobs, business and families here”.

Labour has already promised to take action to stop migrant labour undercutting home-grown workers, by increasing fines for paying below the national minimum wage, closing loopholes in agency worker laws, banning recruitment agencies from hiring only from abroad, and calling for a new law against extreme cases of exploitation.

Mr Miliband said he wants to end an “epidemic of exploitation” which has led to “truly shocking” examples of migrant workers having their wages withheld and being forced to live in appalling conditions.

“When people can be exploited for low wages or endangered at work, it drags the whole system down, undercutting the pay and conditions of local workers,” said the Labour leader.

“We must end the epidemic of exploitation. We must stop people’s living standards being undermined by scandalous undercutting.”

Setting out his new proposals, he said: ” We are serving notice on employers who bring workers here under duress or on false terms and pay them significantly lower wages, with worse terms and conditions.

“We will make it a criminal offence to undercut pay or conditions by exploiting migrant workers.”

Aides said that bringing in foreign labour to undercut the pay and conditions of existing workers will not be sufficient, under Labour’s plans, to secure a prosecution on its own, but it could be used as a piece of evidence of exploitation.

To secure a conviction, evidence will be needed that an abuse of power has occurred and that migrants were employed on significantly different terms to local workers.

Mr Miliband said that, rather than the “false promises” to bring down net immigration offered by the Conservatives or Ukip’s “false solution” of quitting the EU, Labour will seek to offer “clear, credible and concrete solutions which help build a country that works for you”.

But Ukip leader Nigel Farage mocked what he said was “Mr Miliband’s latest relaunch” by posting a picture of the gesticulating Labour leader with a caption reading: “Immigration? Uh – quick, look over there!”

The 33-page leaked Campaigning Against Ukip document warns Labour campaigners that having immigration become a major talking point on the doorstep “does not translate into electoral advantage for us”.

“Immigration is the issue people most often cite when explaining support for Ukip,” it explains.

“It does not, however, follow that campaigning on immigration issues and emphasising our policies in our conversations with electors is always the correct response.”

While it was important to listen to concerns, it went on, “our focus instead must be moving the conversation on to issues where we have clear policy which tackles the problems people are worried about, whether they express those concerns through the prism of immigration or not”.

Campaigners should identify Labour strengths and “encourage them to think more about this … than immigration”.

The document exposes the level of disquiet that exists at the top of the party over the threat posed by Ukip, not least in former Labour strongholds in coalfield communities.

Alongside detailed constituency maps pinpointing areas where Ukip switchers are most likely to live, it warns that Labour supporters are being lured away because they “feel that the party has left them behind in pursuit of better-educated, middle-class, white-collar voters”.

A Labour spokesman said: “This document sets out clearly how candidates and activists will explain our policies on immigration and seek to explain how they fit into an overall vision for a country that works for everyday working people, not just a few.”

Shadow work and pensions secretary Rachel Reeves said she had not seen the document, but claimed the comments about moving voters’ conversations away from immigration had been “taken out of context”.

“This is clearly something that Labour is talking to voters about, and it is our second pledge after our pledge on the deficit last week,” she told BBC Radio 4′s Today programme.

“I haven’t seen the document but my understanding is those lines have been taken out of context.

“Some people have immigration as their number one concern. Other people do not. I think it is important when we are out campaigning that we focus on the issues that people are raising with us.”

Shadow home secretary Yvette Cooper said she did not sign off the leaked document.

Ms Cooper told Radio 4′s The World At One: “I’m afraid the document was wrong on this and it doesn’t reflect what we are actually doing.

“What Ed is talking about today is making a pledge on immigration the second pledge that we are setting out for our manifesto for the campaign for the general election, because we know that the three things that people have most concerns about are around the economy, around immigration and around our National Health Service.

“I’m not taking it too seriously and I don’t think you should take this document too seriously because it doesn’t reflect what we are actually doing.”

Labour MP Simon Danczuk said he was “concerned” about the document, telling The World At One: “I meet people on the doorstep and they talk about the NHS being under strain from immigration, they talk about housing and the pressure from immigration. In this part of the world, when people talk about crime, they sometimes mention trafficking, grooming gangs, sham marriages. This is the reality of it.

“So you can’t really shine a lot on your other policies without talking about immigration as well.”

The Rochdale MP warned that Mr Miliband risked appearing “anti-business” by focusing on employers’ responsibilities.

“My concern primarily is that often when Labour speak about immigration, we talk about the emphasis being on employers abiding by certain rules. I think it comes across as anti-business at times,” said Mr Danczuk.

“I think it’s important for government to do more in terms of immigration, not just to put it all on employers and on businesses. I’m a little concerned that the message we often send out is about employers and businesses doing more on immigration, when really it’s down to the government and agencies of the government to enforce and control immigration.”

TUC general secretary Frances O’Grady said: “This Government’s opposition to basic rights at work and unwillingness to enforce those that exist has helped make the UK the exploitation capital of Europe.

“We welcome these proposals to crack down on those who use migrant workers to undermine the existing workforce. Free movement of workers shouldn’t let unscrupulous employers get something for nothing. Everyone should be paid a decent wage for doing a decent job.”