Timeline: Campaigns for a European Union referendum
The Conservatives say they will hold a referendum on the UK's membership of the European Union by 2017 if they win the election. It is the latest step in the long history of campaigning for such a vote.1970s:
1 January 1973: The UK joins the European Economic Community (EEC). Negotiations were conducted by Tory Prime Minister Edward Heath
1974: Labour, under leader Harold Wilson, promises a referendum on whether to remain in the EEC in the party's election manifesto
6 June 1975: The public endorse the UK's continued membership of the EEC, with 67% of people voting to stay in at a referendum1980s:
1983: In their election manifesto, Labour, under leader Michael Foot, pledge to begin negotiations to withdraw from the EU "within the lifetime" of the following Parliament. Labour lose the election
1989: Margaret Thatcher signals the UK will join the European Exchange Rate Mechanism. She resigns 18 months later amid internal divisions over Europe and other issues1990s:
1992: European leaders sign the Maastricht Treaty, creating the modern day European Union. The UK exits the European Exchange Rate Mechanism
1993: Tory rebels fail in campaign for a referendum on the Maastricht Treaty. Parliament approves the treaty but only after John Major is forced to call a vote of confidence in his government. Denmark and France are among countries to hold a referendum
1996: Businessman Sir James Goldsmith launches the Referendum Party to campaign for a public vote on the UK's membership of the EU. It secures 3% of the vote at the 1997 general election
1997: In their election manifesto, Labour say a yes vote in a referendum is a "pre-condition" for Britain for joining the single currency.
1999: The euro is launched. The UK opts out2000s:
2004: Labour Prime Minister Tony Blair says a referendum will be held on ratification of the European Constitution Treaty but does not name a date for the poll
2005: Labour, the Conservatives and the Liberal Democrats all promise a referendum on whether to ratify the EU Constitution in their general election manifestos. France and the Netherlands reject the proposal in referendums
2006: The cross-party Better Off Out Group, seeking the UK's withdrawal from the EU, is launched
2007: The European Commission proposes a replacement treaty, which comes to be known as the Lisbon Treaty. The Labour government says it is a different document, amending not overwriting existing treaties, and a referendum is not needed. Conservative leader David Cameron gives a "cast-iron guarantee" to hold a referendum on any treaty emerging from the Lisbon process if he becomes PM
2008: Lib Dem leader Nick Clegg calls for an "in-out" referendum on UK membership of the EU. MPs reject a Conservative call for a referendum on whether the Lisbon Treaty should be ratified by 63 votes. 15 Labour MPs and 14 Lib Dems rebel against their parties
2008: The UK ratifies the Lisbon Treaty. The High Court rejects calls for a judicial review of the decision by Tory MP Bill Cash and businessman Stuart Wheeler. They claim ratification without a referendum was illegal
2009: David Cameron admits he will not be able to fulfil his pledge to hold a referendum on the Lisbon Treaty because it has been ratified by all EU member states. But he says, if elected, no future substantial transfer of powers will take place without the approval of the British people. The UK Independence Party, which puts an in/out referendum on UK membership of the EU at the heart of its programme, comes second in the European Parliament elections, with 16% of votes.2010s:
April 2010: In their election manifesto, the Lib Dems pledge to hold an "in-out" referendum the next time there is a "fundamental change" in the EU's treaty arrangements
May 2010: A new generation of more eurosceptic Conservative MPs is elected to Parliament
February 2011: Tory MP Peter Bone fails in a bid to secure an "in-out" referendum by amending government legislation proposing a referendum in future if big changes are made to EU treaties. Mr Bone said a second referendum on UK membership should be triggered if the public initially vetoed plans to hand more powers to Brussels but his plan to change the Europe Bill is rejected
March 2011: People's Pledge campaign for a referendum is launched.
8 September 2011: A petition calling for a referendum on EU membership, signed by 100,000 people, is handed into Downing Street
12 September 2011: More than 100 Tory MPs meet to discuss how to reconfigure the UK's relationship with Europe in wake of the eurozone financial crisis
17 October 2011: Backbench business committee agrees to hold a Commons debate on EU membership following a request by Tory MP David Nuttall.
24 October 2011: The motion calling for a referendum on EU membership is defeated in the Commons by 483 votes to 111. However, 81 Tory MPs support it and a further two actively abstain - making it by far the largest ever Conservative rebellion over Europe. In addition, 19 Labour MPs and one Liberal Democrat defy their party leadership in urging a referendum.
22 January 2013: In a long awaited speech Prime Minister David Cameron says that if the Conservatives win the next election they would seek to renegotiate the UK's relationship with the EU and then give the British people the "simple choice" in 2017 between staying in the EU under those terms or leaving the EU. His speech comes against a background of polls suggesting UK Independence Party support at 10%.
5 July 2013: The Conservative backbencher James Wharton brings forward a bill to enshrine in law his party's pledge to hold an in/out referendum in 2017. It passes its second reading by 304 votes to 0. It goes on to clear all its Commons hurdles before falling in the House of Lords.
31 January 2014: David Cameron says the Conservatives will bring back the Private Member's Bill and said he was prepared to use the Parliament Act to force it into law, rather than seeing the Lords block it again.
5 March 2014: It is announced that the BBC is to host a TV debate on Britain's future in Europe between UK Independence Party leader Nigel Farage - whose party is riding high in polls ahead of May's European election and who wants an immediate in/out referendum - and Nick Clegg, whose Lib Dems say they are the only "party of in" when it comes to the EU.
12 March 2014: Ed Miliband writes an article for the Financial Times in which he says that Labour will not hold a referendum on the UK's membership of the European Union unless there are proposals to transfer further powers from London to Brussels.
26 Mar 2014: Lib Dem leader Nick Clegg and UK Independence Party leader Nigel Farage clash in the first of two live debates on whether the UK should be in the EU. The second debate is being broadcast on BBC Two on 2 April at 19:00 BST.