They once proudly painted themselves the party of Europe, commanding the domestic agenda for the evolving union.
Harold Macmillan lodged the first application to join, Edward Heath took Britain in and Margaret Thatcher signed the Single European Act - the treaty from which much of the EU's future integration has flown (she now protests she was misled as to its meaning).
But look at the Conservatives now. Far from being at the heart of Europe - the position John Major once declared was his government's preferred destination - the European issue has been at the heart of the party's problems since the mid-1980s.
At the same time Labour, deeply suspicious of Europe and in favour of withdrawal, began the slow journey in the opposite direction - from antipathy to support.
The trigger for both parties to swap their respective positions was the belief that, with the completion of the single market, it was becoming evident that other members thought it should be more than just a club of trading partners.
Geoffrey Howe: His resignation led to Thatcher's toppling
Before that, it had been precisely the trading-based common market aspect of the EC that Labour had been unable to reconcile itself to. For the Tories, however, this had been the chief justification for membership.
As prime minister from 1979, Mrs Thatcher led European negotiations in robust fashion and made no secret of her growing criticisms of what she called the "Eurocracy" and its interference in the free market principles she believed should have a much freer reign across the EC.
But in any chronology of the Conservatives' descent into Euro-fratricide, September 1988 deserves a special entry.
This is when emergence of the shape of the EU's "social dimension" was spelt out most clearly by European Commission president Jacques Delors when he addressed the TUC.
Bill Cash: John Major's tiny majority meant sceptics like him could apply sharper pressure
His speech played a decisive role in winning over Labour's affiliated trade unions to Neil Kinnock's conversion to Europe.
That same month, Mrs Thatcher used a speech in Bruges to deliver a direct riposte that some see now as a declaration of Euro-war: "We have not successfully rolled back the frontiers of the state in Britain only to see them re-imposed at a European level, with a European superstate exercising a new dominance from Brussels."
The Bruges speech led to the formation of the deeply Eurosceptical Bruges Group, whose influence spread within the party.
The speech also further convinced senior pro-Europeans in her cabinet that she had to be stopped. Ultimately, then, the attitudes Mrs Thatcher expressed in it led to her own downfall.
Calling the shots
Two years later she was forced to resign, her leadership fatally challenged by Michael Heseltine as an almost immediate consequence of Geoffrey Howe's resignation speech in which he attacked her approach to Europe.
Margaret Thatcher: Signed the Single European Act
Like an exiled queen, she became president of the Bruges Group within weeks of her own MPs ditching her at the end of 1990.
The Eurosceptic faction's sway spread within the party and to all levels. It was her successor as prime minister, John Major, who reaped the whirlwind once he returned to Number Ten after the 1992 election.
He did so with a much reduced, 21-seat parliamentary majority - small enough to allow his Euro-rebels to call the shots.
Keeping his party and administration together became the main issue informing his government's dealings with its European partners.
Every compromise to his party's Eurosceptics by the one time Euro-progressive, only appeared to further embolden and encourage the rebels - among them Iain Duncan Smith.
Edward Heath: Took Britain into Europe
The anti-European faction seen at one time as a fifth column within the party is now, though, firmly in charge of it, Mr Duncan Smith having won the Tory leadership contest to succeed William Hague.
But the unbridgeable gulf between the pro and anti-European factions remains.
The Tory leader is a "never" man opposed in principle to ever joining a single currency, whatever the circumstances.
He wants to renegotiate the treaties which took Britain into Europe in the first place.
Marginalised pro-Europeans, among them "big beasts" Ken Clarke, Michael Heseltine and European Commissioner Chris Patten, wait in the wings now but once a euro referendum gets under way, will not stay silent.