MPs will vote next week on whether Britain's continued membership of the European Union should be put to voters in a referendum, it was decided today.
The Commons backbench business committee has ordered a debate on the highly-charged issue for October 27 after more than 100,000 people signed a petition demanding a choice.
Although approval of the motion would not be binding, it would place enormous pressure on David Cameron to respect the will of the Commons and seek the public's verdict.
The Prime Minister, who has expressed his desire to take back some powers from Brussels, is publicly opposed to such an in/out referendum.
Pulling out was "the wrong answer for Britain" he told increasingly vocal eurosceptic Tories at the autumn conference in Manchester this month.
"What most people want in this country is not actually to leave the EU, but to reform the EU and make sure that the balance of powers between a country like Britain and Europe is better," he said - insisting the priority was dealing with the eurozone crisis.
But London mayor Boris Johnson told the conference that giving the public a vote on Britain's relationship with Brussels for the first time since 1975 was "not a bad idea".
"There hasn't been a vote. It seems to me to be that if a reasonable question could be framed and put to the people of this country, I think it is not a bad idea," he said.
A referendum would also place enormous strain on the ruling coalition as the Liberal Democrats are predominantly supportive of the EU.
Nikki Sinclaire, the independent MEP who presented the petition to Downing Street, said: "I'm absolutely delighted. This is an issue which has gone on for too long. We need a resolution to the issue so we can move on.
"It's all about pressure. We are going to put pressure on the MPs to vote for a referendum. The MPs that do not vote for a referendum, we will be talking to their constituents about it.
"The campaign will now go on from here."
UK Independence Party leader Nigel Farage said: "Having this debate in Westminster is a good start, but with all party leaders demanding that their MPs reject the motion, I hold out little hope of a 'yes' vote.
"The timescale is deliberately short to make it hard for people to lobby their MPs, and the space for debate on such a massive issue is limited.
"The real debate is going on out there in the country, in people's homes, businesses and pubs. We know from many polls that a vast majority of people want this referendum, we learn next week how many of the MPs have the courage to support their constituents."