The British people will get another chance to decide on their European future by the end of 2017 — marking one more milestone in a long-troubled relationship.

The planned referendum on Britain's membership in the 28-country European Union following a renegotiation of some of the terms of the country's membership is a key element of the new Conservative government's program.

Prime Minister David Cameron was Friday on the second day of a whistle-stop tour of European capitals, trying to convince leaders to offer concessions, including limits to welfare benefits EU migrants can claim.

Europe's been a source of contention for decades in Britain. The British may love Alpine skiing, the horrors of Scandi-noir drama and the late-night hotspots on the Spanish island of Ibiza, but they have often been ambivalent over being part of a political and economic union with Europe.

Many reasons have been cited for the complex relationship.

Maybe it's to do with Britain's "special relationship" with the United States. Maybe it's just to do with the fact that the British are an island people, wary of the entanglements and shifting alliances that have played out on the European continent since the Norman conquest of 1066, through the Spanish Armada, the Napoleonic Wars and two world wars.

Ironically, it was former British leader Winston Churchill who called for "a kind of United States of Europe" in the grim aftermath of World War II.

But when the fledgling European Coal and Steel Community launched in 1951, Britain was nowhere to be seen. It also opted against joining the six founding nations of what was then the European Economic Community in 1957.

Britain has seemed a land apart, even after it joined in 1973.

Here are some memorable events in Britain's relationship with Europe.

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De Gaulle Says Non — Twice

Though Britain was absent at the EEC's formation, it soon changed its mind. Its ambitions, though, were twice rejected by a former ally — the French president, General Charles de Gaulle.

"Non," he said in 1963, and again in 1967.

De Gaulle, who spent much of World War II in London when France was under occupation, warned his five EEC partners — Belgium, the Netherlands, Luxembourg, Italy and West Germany — that Britain had a "deep-seated hostility" to European integration that could bring about the end of what was then commonly referred to as the "common market." He also worried that in crunch times, Britain would always side with the United States over its continental neighbors.

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1975 Referendum: The People say Yes

Edward Heath, who became Conservative prime minister in 1970, made membership of the EEC a key objective. De Gaulle's successor, Georges Pompidou, was far more amenable to British membership and by 1973 Britain finally joined. However, with the opposition Labour Party increasingly conflicted over Europe, accession would not be smooth.

Labour's leader, Harold Wilson, thought a referendum following a renegotiation would overcome the cracks in his party. That referendum in June 1975, Britain's first-ever national plebiscite, was held after Labour's return to power. A majority of 67 percent said "yes" to the question: Do you think that the United Kingdom should remain part of the European Community?

Though membership was secured, the divides within Labour didn't go away, with many leading Cabinet ministers viewing the EEC as incompatible with the aims of socialism. That fissure, among others, would weaken Labour and pave the way for the election in 1979 of Margaret Thatcher's Conservatives.

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Thatcher's Party Splits over Europe

Thatcher was a keen backer of the 'yes' campaign, even venturing to wear a sweater with the flags of the member countries sewed in. However, her 11 years in Downing Street were marked by growing opposition to Europe.

Though her government backed the creation of the single European market in the mid-1980s, she became increasingly hostile to the move to further integrate European countries.

The appointment of French socialist Jacques Delors to head the executive European Commission, added fuel to her fire. Thatcher and a growing part of the Conservative Party were aghast at Delors' ambition for a single currency.

In a 1988 speech, Thatcher rejected the prospect of a "European super-state exercising a new dominance from Brussels." Not everyone in her party was that hostile, and Thatcher's growing antipathy to Europe prompted the 1990 resignation of her foreign secretary and led to a leadership battle. Thatcher's time was up.

Her successor, John Major, sought to mend fences with Europe, even while keeping Britain out of the single currency — Game, Set and Match, he claimed. His government would soon after descend into conflict over Europe.

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Blair on a Bike

When Tony Blair won in a landslide in 1997, he made Labour a decidedly pro-European party. Britain, he said, would be at the "heart of Europe." He even indicated a willingness to join the euro, which launched in 1999. The image of the young premier on a bike in Amsterdam a few weeks after his election triumph with other European leaders symbolized the new approach.

Blair built bridges initially, but his decision to back the U.S.-led war in Iraq in 2003 put him at odds with French President Jacques Chirac and German Chancellor Gerhard Schroeder. Plans to join the euro stalled and Blair's European enthusiasm hit a roadblock.

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Referendum Redux

With Blair's departure in 2007, pro-Europeans lost a key voice. His successor, Gordon Brown, was more lukewarm while the opposition Conservatives morphed into a primarily Euroskeptic party. In 2011, Prime Minister David Cameron vetoed an EU treaty designed to help stabilize the euro, which was struggling following a debt crisis.

And with the U.K. Independence Party making headway with its demand for a fresh vote on Britain's membership, and its assertion that Britain had ceded too much sovereignty to Brussels, Cameron felt compelled to promise a referendum to bind his party together.

The Conservatives' recent surprise victory has put that referendum in motion. That vote will take place by the end of 2017.