Backgrounder: How Britons decided on stormy "marriage" to Europe in 1975

Maybe it's because it is an island nation, but Britons have always had mixed feelings about greater union with the European mainland.

In 1975, just two years after Britain joined what was then the six-nation the European Economic Community (EEC), a referendum was called to test the feelings of Britons about membership.

By a vote of parliament Britain had joined on Jan. 1, 1973 what was then also referred to as the "Common Market," consisting of Belgium, France, Germany, Italy, Luxembourg and the Netherlands.

Heads of the six nations, on March 25, 1957, had signed the historic Treaty of Rome, establishing the EEC.

Ireland and Denmark, joined at he same time as Britain, with the British Union Flag hoisted above the EEC headquarters in Brussels at the stroke of midnight.

Britain had applied twice in the 1960s to join, but the applications were blocked.

Conservative Prime Minister Edward Heath, who took Britain would later described the move as his greatest achievement in politics. Yet just two years later the then Labor Prime Minister Harold Wilson promised a referendum because of squabbling over the EEC.

On June 6, 1975, the nation -- by a wide margin -- decided to stick with Europe, with 17,378,581 (67.23percent) voting to stay, while 8,470,073 (32.77percent) wanted to leave, on a turnout of just over 65 percent.

Only two parts of Britain voted to leave, the Western Isles of Scotland with 70.5 percent or 8,106 voters, wanting out, while 29.5 percent, or 3,393 voters, wanting to remain.

In Shetland, 3,361 (56.3percent) voted to leave and 2,815 (43.7percent) wanted to stay.

In Northern Ireland, 52.10 percent chose to remain, with 47.90 percent wanting to go. Across Scotland 58.40 percent voted stay, while 41.60 supported quitting Europe.

Veteran Labor politician Tony Benn, the government Industry Secretary in 1975, commented at the time "When the British people speak everyone, including members of Parliament, should tremble."

Whether the population of Britain will cause tremors across Europe with their decision in June will be learned soon enough.

From 1975 the EEC became a collective of nine of the major nations of Western Europe. Today the European Union has 28 members, with more countries waiting in the wings to sign-up. The British people will decide whether their nation will exit. Endit