Ed Miliband has admitted the EU referendum "is in question" as a growing number of senior Labour figures voice concerns that Britain might vote for Brexit.

His comments come after shadow Home Secretary Andy Burnham warned the Remain campaign is facing the "very real prospect" of defeat in the vote in two weeks time.

Their interventions come as prominent Labour backbenchers Dennis Skinner and John Mann announced that they were joining the handful of party MPs who are supporting Leave.

Speaking to the BBC Radio 4 Today programme, former Labour leader Mr Miliband warned that the party has not done enough to make its stance on the EU clear to voters.

He said: "This referendum is in question and that's why the Labour message has got to be heard, and I think so far not enough of our voters have heard that we are for in, and for Remain, and we are for it because economically we are stronger, for workers' rights we are stronger, and tackling the problems we face in the world, we are stronger."

He said the referendum debate has been dominated by "blue on blue" battles and denied it is turning into a "red on red" fight.

He said: "This is an important point - 95% of Labour MPs, every major trade union leader, all ex-Labour leaders and indeed Jeremy Corbyn, the vast majority of our party is for Remain.

"I do think, and I'm calling this out today, the Leave campaign is trying to perpetrate a fraud on Labour voters.

"They are trying to say that we really share your values, whether it's the NHS or workers' rights or fairness in our society, that's what we care about. And we have got to call that out.

"We call that out because economically the cuts that would come from the economic shock that would hit the country will hit Labour areas hardest, because the record of these people in the Leave campaign, if they are going to get out of the European Union, is not to improve workers' rights but to sweep them away."

He brushed aside claims Jeremy Corbyn's past criticisms of the EU have left many voters doubtful over his sincerity on the campaign trail, insisting that the Labour leader is an effective advocate for the Remain campaign.

But he conceded that "some Labour voters don't know where we stand at the moment" and more needs to be done to hammer home the message.

Asked frankly if he thinks there is a real possibility the Remain campaign will lose the vote, he said: "Most people haven't voted in this referendum yet, the result - as I know from the general election - the result is in question.

"I think I got out of the forecasting business after my election, I'm optimistic we can win this election but we have got to get the arguments across. We haven't done enough yet, we have to do more.

"The people need to know where Labour stands, and I know Jeremy believes that, everybody in our party believes that."

His words come after Mr Burnham sharply criticised the party's campaigning, saying it had failed to reach out to traditional Labour voters amid fears that concerns about immigration are driving them to back Leave.

"We have definitely been far too much Hampstead and not enough Hull in recent times, and we need to change that. Here we are, two weeks away from the very real prospect that Britain will vote for isolation," he told BBC2's Newsnight.

And he warned that a vote for Brexit could lead to the disintegration of the UK.

Meanwhile, Mr Mann and Mr Skinner both publicly came out in favour of the Leave campaign.

Mr Skinner told the Morning Star that he was rebelling against the party line as he believed furthering socialist reform would be easier as an independent country.

The veteran left-winger, nicknamed The Beast of Bolsover, said: "My opposition from the very beginning has been on the lines that fighting capitalism state by state is hard enough. It's even harder when you're fighting it on the basis of eight states, 10 states, and now 28."

His opposition also came from concern over the impact a possible US-EU trade deal, known as TTIP, may have on the NHS. His Euroscepticism was not driven by "waving a flag or immigration", he added.

Writing in The Sun, Mr Mann said he now favoured withdrawal as the country had "one hand tied behind our back" when it came to controlling immigration in the EU.

"People have been terrified about talking about immigration. But on polling day they are going to get a big shock across the country," he wrote.

"They are going to get a big shock about how Labour councillors vote, they will get a big shock about how Labour members vote."

The warnings come as senior Labour figures try to inject new momentum into the party's campaign effort.

Former cabinet minister Yvette Cooper will release a report warning of the damage facing Labour heartlands if the "far right of the Conservative Party" gets its way.

And deputy leader Tom Watson will release analysis indicating Brexit could result in £18 billion of welfare cuts and tax hikes as the Tories impose tighter austerity measures.

A Vote Leave spokesman said: "As support drains away from the Remain campaign, they are getting ever more desperate and hysterical with their fanciful Leave predictions.

"We need to vote Leave if we want to take back control of our economy, borders and democracy."