LONDON (Reuters) - A future Labour government is unlikely to hold a referendum on Britain's membership of the European Union (EU) this decade, party leader Ed Miliband pledged on Wednesday.

In a political gamble that lowered the chances of Britain leaving the bloc, Mr Miliband, who would be prime minister if Labour wins the 2015 election, said he would only hold an in-out vote if there were to be substantial transfers of powers from London to Brussels.

That is unlikely at this stage, particularly since future European political and economic integration would probably come within the euro zone, of which Britain is not a member.

Mr Miliband's pledge, appearing first in the Financial Times newspaper and later to be outlined in a speech, contrasts sharply with current Prime Minister David Cameron's promise to to try to reach a new settlement with the EU before holding an in/out vote by the end of 2017.

"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," Mr Miliband wrote in the newspaper.

"There are no current proposals - from either the EU or any member state - for a further transfer of powers from Britain," he said. "It is unlikely there will be any such proposals in the next parliament."

By offering only a distant and conditional referendum, Mr Miliband is seeking to turn Mr Cameron's EU strategy against the ruling Conservatives: Mr Miliband is betting that Europe is much less of an issue than the economy for most British voters.

Mr Miliband said Mr Cameron's Conservative party had a "damaging obsession" with Europe that was spooking businesses. The Labour party, by contrast, wanted to work for reform from within the 28-member bloc.

The 44-year-old Labour leader is gambling that Conservative focus and divisions over Europe will turn voters off Mr Cameron in 2015 and that Labour's referendum pledge will please business which has criticised Labour for its tax and energy policies.

Mr Miliband, whose party currently leads in opinion polls, said Mr Cameron's "arbitrary" timetable for an EU vote would distract from dealing with Britain's economic challenges and that Mr Cameron had no support in European capitals for his renegotiation.

Mr Cameron, who is under pressure from eurosceptics in his Conservative party and the anti-EU UK Independence Party, says Britain can reshape its EU ties, though he has so far garnered only limited backing for his plans among fellow leaders.

"Only the Conservative Party can guarantee and deliver that in-out referendum," said Mr Cameron, who has charged that Labour is afraid of giving British voters the chance to have their say on Europe.

Mr Cameron's Liberal Democrat coalition partners are outspokenly pro-EU and would have no problem with Labour's position if they were in a future coalition with it.

Mr Miliband used the waving of Europe's azure-and-golden-starred-flag by some Ukrainian protesters in Kiev to argue that voters should not forget the European Union symbolised peace and prosperity for many after centuries of European strife.

But the Labour leader also cautioned that the EU's reputation was at a low ebb: he said EU leaders should do more to build a better economy and address voter anxiety over immigration.

"If Britain's future in Europe is to be secured, Europe needs to work better for Britain," he wrote. "Britain needs to work more effectively for change within the EU."

"Europe should also do more to address anxieties about immigration," Mr Miliband said, adding that there was considerable voter concern that "the EU is intent on an inexorable drive to an ever closer union".

Opinion polls show about 40 per cent of British voters want to stay in the EU while about the same proportion want to leave, though polls also show widespread hostility to immigration and dissatisfaction with established political parties.

Europe was the undoing of the last two Conservative prime ministers, Mr John Major and Mrs Margaret Thatcher, but polls show that the economy, immigration, health and welfare trump Europe as an issue for voters.

Mr Miliband said that a Labour government would find it considerably easier to achieve reform inside the EU without having to attempt to convince 27 other EU member states to rewrite a European treaty.

He said German Chancellor Angela Merkel, the EU's most powerful leader, had refused to support Mr Cameron's plans for fundamental European reform during a visit to London last month.

Dr Merkel, who has said that she wants Britain to stay in the EU, does favour some EU treaty change. But she sees treaty change as much more limited in scope than Mr Cameron and as a way of deepening euro-zone integration.

"She explained that he needs unanimous backing to get a new treaty. It is clear he has none," Mr Miliband said.