If historian John Ramsden is right, Euroscepticism will return the Tories to power, writes Brian Brivati. But, as David Baker observes, Europe is also the issue that has polarised the party.
* 1979-1983: High point of Labour Euroscepticism with conference, and later manifesto, commitment to withdraw from European Community without a referendum. Departure of future leaders of SDP.
* 1983: Neil Kinnock's leadership effects slow reversal, assisted by Margaret Thatcher's monopoly of office and growing anti-Europeanism. Labour sceptics marginalised. Unions also converted to Europe after Jacques Delors's 1988 address to TUC outlining advantages of Europe's social dimension.
* MID 1980s - 96: Conservatives, once Britain's "party of Europe", divided. Cabinet ministers including Mrs Thatcher propelled from office over the issue. Maastricht backbench rebellion among most damaging suffered by the party.
Major resigns leadership and stands for re-election mid-term, challenging critics to "put up or shut up".
* 1997: For general election, a third of Conservative candidates issue personal manifestoes ruling out single currency. "Beef war" raging between London and Brussels.
1997 May - October: New Labour ready to extend majority voting, restrict the national veto in some areas, enlarge role of European Parliament, and abandon boycott of Social Chapter. Tony Blair persuades EU leaders to postpone indefinitely a European defence union and extracts promise that Britain could postpone joining full EMU until 2002 and still have a say in key policy decisions.
William Hague defeats rival Ken Clarke on a Eurosceptic platform. Imposes "No single currency for two years" formula on shadow cabinet. Peter Temple-Morris threatens resignation. Ian Taylor resigns from Conservative front bench. Michael Heseltine warns of "Eurosceptic bacon slicer always trying to take the argument further".
* OCTOBER 1997: Cracks begin to appear in Labour's Euro policy. Britain fails to gain veto over "Euro-X" committee decisions on implementation of single currency. Amid internal dissent, Labour's manifesto pledge to hold referendum on single currency effectively postponed until after next election.
* JANUARY 1998: Letter to the Independent signed by Tory stars calls for sterling to join single European currency "at the earliest opportunity". Hague calls them "yesterday's men".
* AUGUST 1998: Multi-millionaire and former Tory Paul Sykes announces nationwide multi-media anti-Euro publicity blitz, from January 1, 1999, for "as long as it takes".
* 1998: At Tory Party conference, ballot of party members on ruling out the single currency for two parliaments gets 84 per cent backing. Hague urges party to "move on" to attacking Labour. But Tory "big beasts" - Heseltine, Clarke, Patten, Gummer, Howe, Brittan, Heath and Whitelaw - continue dissent. At fringe meeting, Clarke accuses Lamont of spouting "paranoid nonsense". Heseltine denies he will leave the party over Europe but dismisses ballot as an "irrelevance" and speaks of sceptics as "cancer at the heart of the party, which is making it fall apart". Hague refers to "last roar of the dinosaurs".
* THE FUTURE: If the Euro is a success, there is likely to be pressure for Britain to join and for a referendum after the next general election. If Labour wins the election, it is also likely to win a referendum. But the anti-Euro stance of The Sun newspaper could be a problem.
The Thatcherite right is swinging behind the anti-Euro Portillo, who is poised to seek the leadership if Hague loses the next election. If Portillo's line is adopted, pro-Europeans would be forced to leave.
David Baker is reader in British politics at Nottingham Trent University.