Ed Miliband has finally showed his cards in the grand political game of a referendum over British membership with the EU - effectively ruling out a poll.
Labour will only guarantee a poll if Brussels demands fresh powers, but there is no promise to match David Cameron's promise of a decisive poll in 2017.
The Labour leader stressed his determination to reform the EU if elected in 2015, and pledged a legal lock that would guarantee an in-out vote if Westminster was asked to hand over more control.
But he made clear, in an article for the Financial Times, that he believed that was "unlikely" in the next parliament.
Within minutes of the piece being published, the Prime Minister responded that the only way of securing an in-out referendum was to back the Conservatives.
The announcement has had a mixed reaction on social media:
So @Ed_Miliband is to announce he's found another way of denying British people an EU referendum. Why bother getting out of bed to say that?— Jonathan Isaby (@isaby) March 12, 2014
Miliband decision is a no-brainer. What mug becomes PM only to spend 2 years mired in EU stuff, then hold referendum as unpopular incumbent?— Janan Ganesh (@JananGanesh) March 11, 2014
So Miliband's position is now that he would vote in favour of literally any handover of new powers to the EU. That sounds popular.— Mark Wallace (@wallaceme) March 11, 2014
Miliband, who will flesh out his position in a keynote speech later, acknowledged that people had "concerns" about the EU and said Labour's "agenda for change" would seek to return "more control to national parliaments".
"It is important to emphasise that there are no current proposals - from either the EU or any member state - for a further transfer of powers from Britain," he said. "Therefore it is unlikely there will be any such proposals in the next parliament.
"But the British people know that the history of the EU, as well as uncertainty about precisely what a changing Europe and further integration in the eurozone might involve, means that a further transfer of powers remains possible.
"So in a speech today I am announcing that the next Labour government will legislate for a new lock: there would be no transfer of powers from the UK to the EU without a referendum on our continued membership of the EU.
"This would not just be a referendum on the narrow question of whether to allow a transfer of powers from Britain to Brussels; as we have seen in other countries, such votes are too easily ignored.
"This position, setting out the conditions in the next parliament under which a Labour government would hold an in-out referendum, offers the British people a clear choice at the next election."
Miliband launched a stinging attack on Cameron for being "driven by weakness" to appease right-wingers and promise an in-out referendum by 2017.
"David Cameron has committed the Conservatives to a major renegotiation of Britain's relationship with Europe on an arbitrary timetable for a 2017 referendum about Britain leaving the EU," he wrote.
"But he is a Prime Minister who cannot tell us the nature of his renegotiation strategy or even if he will campaign to keep Britain in Europe.
"Mr Cameron's position, riven with doubt and driven by weakness, means his priority after 2015 would not be tackling the cost of living crisis or creating jobs and prosperity. Instead, a Conservative government would be dominated by an all-consuming and damaging obsession within his party about whether Britain should leave the EU.
"You do not need a crystal ball to predict the consequences of such a state of affairs; you only need to read the history of John Major's government."
Miliband added: "Labour's position on Europe, by contrast, is clear and principled: we strongly believe Britain's future is in the EU.
"And my priorities for government after the next election are very different from those of the Conservatives. Labour will focus on dealing with the cost of living crisis by building a better economy so that people can look forward to a better future for their children. An arbitrary timetable for a referendum on leaving Europe would damage our ability to deliver on these priorities."
Miliband said he recognised the "reputation of the EU is, with reason, at a low ebb". "If Britain's future in Europe is to be secured, Europe needs to work better for Britain," he added.
The Labour leader called for swift action to complete the single market, and for the EU to "address anxieties about immigration".
"We need fairer rules on what happens when people move here from another country and action to prevent a race to the bottom, where workers already here have their pay or conditions undercut," he said.
"A Labour government would work with our EU partners to lengthen the existing transitional arrangements for countries joining the EU so that their citizens have to wait longer before gaining rights to work here.
"There should be reforms to rules allowing people to claim child benefit or child tax credit when their children live abroad.
"And we should look at ways to make it easier to deport people who have recently arrived in this country when they commit crime."
The legal lock proposed by Miliband would effectively upgrade the one introduced by the coalition which guarantees a referendum before any powers are transferred.
Labour's position aligns it closely with the Liberal Democrats on Europe, offering common ground for any potential negotiations about forming a joint government in 2015.
Posting on Twitter last night, Cameron said:
1/2 By his own admission, Ed Miliband says it's unlikely there'll be an in-out referendum on Europe under Labour.— David Cameron (@David_Cameron) March 11, 2014
2/2 Only the Conservative Party can guarantee and deliver that in-out referendum.— David Cameron (@David_Cameron) March 11, 2014
Labour's move was welcomed by Sir Martin Sorrell, head of advertising and media giant WPP.
Sir Martin said the "balance of probability" was that there would be no transfer of powers and therefore no national poll.
"I would say not having a referendum is better than having one," he said. "Having a referendum creates more uncertainty. The last thing we need is more uncertainty."
He added: "I think it is beneficial because it removes one of the 'grey swans' that we are worried about."
Former foreign secretary Jack Straw, seen as a Eurosceptic in the Labour ranks, said: "He is right that the priority of the next Labour government should not be an all-consuming debate about leaving the EU. Unfortunately that is only being offered by David Cameron out of political self-interest, not the national interest.
"But Ed Miliband is also right that in the event of a transfer of powers from Britain to Brussels we should give the people a vote in an in-out referendum. This offers reassurance not only to business and millions of workers whose jobs depend on Europe but also allays the fears of those who are uncomfortable with moves towards ever closer union."
However, fellow Labour MP John Mann said he still hoped Miliband would go further and commit to an in-out referendum even if no power transfer is on the table.
"Certainly I've polled very (extensively) Labour votes in my area, and without question, they're more hostile than they were to the European Union - significantly more so - and I think that we need to be in touch and we need to be trusting the people," he told BBC Radio 4's World Tonight.
"So I hope that over the next few months he'll go further and say that the Labour Party's going to trust the people and let the people have a say on this."