Here is a guide to the Conservative Party's new policy on Europe - and why it is causing controversy.
What has David Cameron announced?
The Conservative leader has come up with a three-point plan for dealing with the EU if, as the polls suggest, he becomes prime minister next year:
• Ban the transfer of further power to the EU without a referendum
• Introduce a Sovereignty Bill to ensure "ultimate authority" remains in the UK
• Start negotiations to bring back powers from Brussels over employment law and criminal justice - and push for a complete opt-out of the Charter of Fundamental Rights
What is the purpose of this policy?
Mr Cameron says he wants to prevent Britain from becoming part of a federal Europe or "superstate". His critics say he is trying to sound tough on Europe to head off a civil war with Eurosceptics in his own party.
Why has he announced this now?
The Tory leader says his measures will enable Britain to protect its own national interests, now that the Lisbon Treaty - which he argues will bring about a major transfer power to Brussels - is about to come into force.
Why not just hold a referendum on the Lisbon Treaty?
The Conservatives have spent the past few years calling on the government to hold a referendum on the Lisbon Treaty. But now that it has been ratified - and is due to come into force on 1 December in all 27 EU nations - Mr Cameron says a public vote would be pointless, because the treaty is irreversible.
So has he broken a promise to voters?
Mr Cameron insists that he never promised a "post-ratification" referendum - and that he had always made clear he would come up with a new policy if the treaty became law before he gained power. But his critics point to a 2007 article in which appeared to give a "cast iron" guarantee of a referendum.
How has this gone down in the Conservative Party?
It has caused anger among Eurosceptics - a powerful lobby in the Conservative Party who thought they could rely on Mr Cameron's support. They either want a post-ratification referendum on the Lisbon Treaty or a referendum on Mr Cameron's demands for powers back from Brussels. But Mr Cameron has explicitly ruled out holding a referendum on Europe "for the sake of it".
So is Mr Cameron facing the kind of "civil war" on Europe that has split his party in the past?
Shadow Foreign Secretary William Hague says the party had always expected a few dissenting voices but he insists that the vast majority of Tory MEPs and MPs are fully behind the new policy. And it seems likely that any revolt over Europe will be put on hold until after an election to avoid scuppering the party's chances of forming a government.
How has the policy gone down in the rest of Europe?
There has been a backlash from some countries, with France's Europe minister Pierre Lellouche being the most outspoken critic, although he said his descriptions of Tory policy as "pathetic" and the product of a "bizarre autism" on Europe were down to bad translations. Minsters in Poland, the Netherlands and the Irish Republic have warned that no member state would reopen negotiations in the way Mr Cameron wants. Belgian's foreign minister said the comments should be treated as "political rhetoric". German Chancellor Angela Merkel said European integration could not be "jeopardised".
So how difficult is it to get powers back from the EU?
Very difficult, as Mr Cameron has acknowledged. He would need the agreement of all 27 member countries, who might not take kindly to Britain reopening negotiations on policies already agreed in previous treaties. He has attempted to reassure other EU nations by saying he is not seeking a "massive bust-up" and that negotiations to repatriate powers are a long-term aim.
Is it possible to guarantee British laws will have sovereignty over EU laws?
This is something of a legal minefield. Mr Cameron has said he wants to emulate Germany, where the German constitution is ultimately supreme. It would not mean striking down individual pieces of EU law, he adds, but would provide ultimate constitutional "safeguards" against attempts by EU judges to "erode" British sovereignty. However some constitutional experts believe the European Court of Justice would have to remain the highest authority.
What about Mr Cameron's guarantee of a referendum on future treaties?
Mr Cameron says he wants Britain to be like Ireland, where any transfer of power to Brussels has to be approved by a referendum. He says he would amend the 1972 European Communities Act to make this happen. He has called on the other parties to say they would never seek to overturn this, but there is no guarantee they will listen to him.