LONDON (REUTERS) - Britain took a step towards holding a public vote on whether it should remain in the European Union (EU) when members of parliament backed an effort to enshrine the referendum promise in law.

Prime Minister David Cameron is backing the draft legislation as a way to help bridge damaging divides over Europe in his Conservative party. It is also designed to counter the threat of euro-sceptic voters defecting to the anti-EU UK Independence Party at the next general election in 2015.

The bill, promising a referendum before the end of 2017, passed through the lower chamber of parliament on Friday despite opposition lawmakers' attempts to filibuster it.

Because neither the Liberal Democrats, Mr Cameron's junior coalition partners, nor the opposition Labour party support the call for a referendum, the proposal is being pushed through via an unorthodox legislative channel which imposes strict time limits on debates and reduces its chances of becoming law.

Nevertheless, after a major internal rebellion over Europe earlier this year the bill appears to have helped Mr Cameron unite his party over an issue which has undermined previous administrations and dented the Conservatives' public appeal.

Mr Cameron supports Britain remaining part of the EU, but wants to renegotiate the country's role in the 28-nation bloc. Some hardliners in his party remain deeply sceptical of the benefits of Britain's membership.

The bill still needs to be approved by lawmakers in the upper chamber, where it is expected to encounter similar resistance. It could also be repealed by the next government if the Conservatives lose the 2015 election.