Labour has dropped its opposition to a referendum on the UK's membership of the European Union.
Before his general election defeat, Ed Miliband, as party leader, had refused to hold an in/out vote amid concerns it would damage the UK economy because of the uncertainty it would create.
But the party's acting leader, Harriet Harman, and shadow foreign secretary Hilary Benn, now say Labour believes people want to have a say on Britain's relationship with Brussels.
It means the opposition will give the green light to the Conservatives' planned referendum bill for a nationwide vote before the end of 2017.
In an article for The Sunday Times, the pair wrote: "We have now had a general election and reflected on the conversations we had on doorsteps throughout the country.
"The British people want to have a say on the UK's membership of the European Union. Labour will therefore now support the EU referendum bill when it comes before the House of Commons."
Labour will campaign for Britain to remain in the EU and will press David Cameron to achieve reforms on migration and welfare as part of his renegotiation, according to Ms Harman and Mr Benn.
"The Labour Party doesn't want to see the UK stumble inadvertently towards EU exit. We will make the case for our continued membership," they wrote.
"The notion that Britain's future prosperity and security lies in shutting itself off from this market... makes no sense."
The move comes as Mr Cameron unveils plans for legislation in the Queen's Speech to hold a referendum to "give people the chance to finally decide whether they want to remain in the EU or not".
Meanwhile, former deputy prime minister John Prescott has thrown his weight behind Andy Burnham in the race for the Labour leadership.
Lord Prescott compared Mr Burnham to Tony Blair, claiming the former health secretary showed many of the "skills and qualities" demonstrated by the ex-prime minister.
The high-profile endorsement of Mr Burnham will come as a further boost to the bookmakers' favourite for the leadership.
