At Ipsos MORI, we have been asking people in Britain how they would vote in a referendum on membership since 1977. During this time, both pro- and anti-European views have spent time in the majority – but there have been some dramatic swings from side to side.

The UK’s testy relationship with a united Europe goes back further, to the early 1970s when Ted Heath’s government took Britain into the European Economic Community without a vote on January 1 1973. Gallup polls initially found the public almost evenly divided on the decision, but by the start of the following year there was a two-to-one majority believing the country had been wrong to join.

The Labour leader, Harold Wilson, who became prime minister for the second time after the February 1974 general election, promised a referendum on whether Britain should remain a member – but first, he was going to renegotiate the terms of British membership. Sound familiar?

In February 1975, Gallup found that 41% of people said they would vote to leave in an immediate referendum and only 33% to stay in. But Gallup also asked a follow-up question: how would people vote if the government negotiated new terms for UK membership and said that they thought it was in Britain’s interests to stay in? In that case, it turned out that 50% would vote to stay and only 22% to leave – an 18% swing.

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And that, of course, is what happened. In March 1975, the renegotiation was completed, parliament endorsed it and all the major party leaders recommended that Britain should stay in. In June, the voters opted by 67% to 33% to do so. (The final Gallup poll had forecast a 68-32 result.)

Growing dissatisfaction

It was soon after this that MORI began to publish regular polls in the newspapers, including periodic polls on membership of the European Community – or, as we called it to reflect the universal usage of the time, the “Common Market”.

As James Callaghan replaced Harold Wilson and his government slid toward eventual defeat in the “Winter of Discontent”, the Common Market became steadily less popular. By March 1979 the voters were clearly regretting their 1975 decision, with 60% saying they would vote to leave in a referendum and only 32% to stay. A year later, with Margaret Thatcher now prime minister, the gap was even wider: 65% to 26%.

Opposition to Britain’s membership of the European bloc has never subsequently reached the levels at which it peaked in the first years of the Thatcher premiership. It was the Labour Party which was committed to leaving in the early 1980s. Thatcher argued for, and eventually achieved, changes to the European Community budget involving substantial rebates to Britain which reduced the level of the country’s net funding contribution. The public warmed once more to the communities: opinion was definitely in favour, 47% to 39%, in 1987.

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After this, “get out” was not ahead in a poll again until 1999 – although the gap was very narrow throughout the run-up to Tony Blair’s first election victory in 1997. But that is not to say that the 1990s were a period of broadly stable support for the European project. European issues were central to domestic political debate in Britain in this period, causing bitter divisions that were a crucial factor in condemning John Major’s government to certain defeat to Blair.

Our many polls at this time suggested that the lead of those wanting to “stay in” reflected a willingness to remain in a Common Market but that political and monetary union across Europe were much less popular prospects. In all the time we polled on joining the single currency, from 1991 until 2007, we never in even a single poll found more people in favour than opposed.

In the ten years that Tony Blair was prime minister, British attitudes to the EU fluctuated between reasonably comfortable majorities for staying in and narrow leads for the “get out” camp. At one point there was a swing of 12% in just three months, from a 53%-32% lead for “stay” to 46%-43% in favour of “leave” between June and September 2000 – as Blair was telling voters that Britain should be playing a role “at the heart of Europe”. This was just after the launch of the euro, which the British public felt had not been a success and would continue to fail, and after Denmark voted against joining it.

But the biggest factor in this shift may have been distrust of the then-chancellor of the exchequer, Gordon Brown.

Our only poll on EU membership during Brown’s own premiership, taken in September 2007 before the shine had worn off his “honeymoon period” and before the global financial crisis, found the public once more in favour of staying in by a wide majority. The EU had recently dropped its attempts to force Britain to replace its last few Imperial measurements with metric ones, and most of the public seemed to be pleased with this, although few admitted it made much difference either way to whether they supported EU membership.

Reaction to European expansion

More importantly, though, this was before the introduction of a new dimension into the argument – that of the effect of EU membership on immigration policy. Poland had joined the EU in 2004 and that had immediately been followed by an influx of Polish workers into Britain under laws allowing free movement of labour. Britons had been strongly in favour of Poland joining the EU after the fall of the Berlin Wall, but when it came to the point, some proved to be much less keen on Poles coming to Britain to take jobs.

Nevertheless, even though immigration was already becoming prominent among the “most important issues facing the country” as measured in our Issues Index polls, few were yet explicitly making the link with EU membership.

Under Cameron’s premiership, the polls have swung first against EU membership then more recently in its favour. From the 2015 general election to May 2016, all of our polls found more wanting to remain than to leave; but our poll in the first half of June had “leave” back in the lead. But as the history of British attitudes to Europe tells us, such swings are by no means unprecedented, and there is no guarantee the lines may not cross back again.