The UK’s opposition Labour party is considering matching the Conservative’s offer of an “in/out” referendum on EU membership in a marked policy shift ahead of the next UK general election in 2015. A decision could be announced at Labour Party's annual conference in Brighton later this month, EURACTIV understands.

Prime Minister David Cameron this year (23 January) promised Britons a simple ‘in/out’ referendum choice on whether to stay in the European Union if he wins the next election, scheduled for 2015.

Cameron said the Conservative party would campaign in the 2015 election with a pledge to renegotiate Britain's EU membership and then put the resulting deal to a referendum, possibly in 2017.

>> Read: Cameron takes gamble with in/out EU referendum pledge

Labour is unlikely to offer the same formula, but policymakers with the party have told EURACTIV that party leader Ed Miliband may instead offer to convert a “referendum lock” on EU laws into an “in/out” referendum on Britain's European Union membership.

The so-called “referendum lock” is a policy of the Conservative and Liberal coalition government, unopposed by the Labour party. It states that where any substantial piece of EU law affecting the UK constitution arises, citizens will be offered a referendum on whether to accept it.

Labour party divided over how to proceed

But while Labour supports the "referendum lock", the party does not stipulate whether it would offer citizens an "in/out" option.

Some Labour strategists fear that Conservatives will exploit the lack of an "in/out" choice offered by Labour as a weakness in the run up to the election. Shadow finance minister Ed Balls believes that Labour should offer an “in/out” referendum at an earlier date than Cameron, which would probably take place in 2017, to out-flank the Conservative prime minister.

The Labour party is divided over the issue and it seems unlikely that Ed Balls's argument will prevail, however, EURACTIV understands. Simply converting the referendum lock into an "in/out" choice, without giving a precise date, seems to be favoured amongst a majority policymakers in the party. Such a referendum would be triggered if a change in the EU treaty came under consideration.

Announcement could come at Brighton conference

Miliband could make such an announcement during the party’s annual conference in Brighton later this month (22-25 September), where he is ready to unveil policies to lay the ground for the general election in 2015.

Cameron’s referendum pledge depends on him winning the next election at a time when the Conservative leader is currently trailing the opposition Labour party in opinion polls, and governing through a fractious coalition with the pro-European Liberal Democrats.

Cameron said he supported Britain remaining in a looser EU, centred around the single market for goods and services, which British companies want to safeguard.

The UK Conservative leader dismissed suggestions that an in/out referendum on Europe threatened to create business uncertainty, ignoring US warnings over Britain's role in the European Union.