Even in 2016 – before Turkey’s latest turn towards authoritarianism – the chances of the country joining the EU before 2030 were remote. Yet this did not prevent Vote Leave from claiming towards the end of the referendum campaign that Turkey was poised to join. This unfounded claim, writes James Ker-Lindsay (LSE), played into voters’ existing worries about immigration. It may even have swung the result.

More than a year and a half after the EU referendum, debate still rages as to what exactly led 52% of the population to vote for Brexit. While many argue that sovereignty was the issue that resonated most with Leave voters, others point to the claims about the amount of money that would supposedly be saved – and thus put into public services – if Britain left. Whatever the merits of these arguments, there can be no doubt that for a significant proportion of British voters the question of immigration was at the forefront of their decision.

Although EU membership had not traditionally been as great a concern for British voters as many suppose, the question of immigration became steadily more important from the mid-2000s onwards. Britain, unlike many other EU members, did not institute transitional controls on freedom of movement following the so-called ‘Big Bang’ enlargement of the EU in 2004. Early predictions of a relatively small number of arrivals proved to be way off the mark. By 2011, the number of people residing in the UK who had been born in Poland was officially 579,000. This was the second largest foreign-born community in Britain, after those born in India (694,000).

Growing concern about immigration, particularly in Eurosceptic rural England, was effectively exploited by UKIP in its campaign against British membership of the EU. In 2014, it won the largest share of the vote (26.6%) in European Parliamentary elections – a result that eventually prompted David Cameron to begin his ill-fated effort to renegotiate Britain’s place in the Union, and then hold a referendum on its continued membership.

In early 2016, as the country prepared for the formal launch of the referendum campaign, it was very telling that UKIP continued to keep up its focus on immigration, airing a political broadcast focused solely on the prospect of Turkey’s membership of the European Union. In a video that received widespread criticism for its racist and Islamophobic undertones, UKIP claimed that Turkey would join the EU by 2020 and that as many as 15 million people would leave the country for the EU in the first ten years of its membership.

Of course, to anyone who was following Turkey’s accession process, these claims were unfounded. Although Turkey had begun accession talks in 2005, the pace of progress had slowed dramatically. In fact, increasing authoritarianism in the country had effectively put paid to any prospect of Turkish membership. Even if the country radically changed course, it seemed inconceivable that it could possibly join any time before 2030. And even if it did join, it would seem almost certain that the EU would institute a lengthy transitional control on freedom of movement.

At first, the official Vote Leave campaign conspicuously avoided the issue of immigration. Instead, it focused on economic and sovereignty arguments. However, as these were increasingly and effectively challenged by the Remain campaign, they too shifted the debate towards Turkey. This resulted in a controversial poster campaign claiming that ‘Turkey (76 million people) is joining the EU’.

By this point, even those Brexit-supporting Conservative MPs who had previously strongly advocated Turkish membership of the EU were lining up to highlight the threat this would pose to Britain. The most prominent of these was Boris Johnson, who even wrote a letter to the Prime Minister asking for his guarantee that Turkey would never join the EU. (After the referendum, he again changed his mind and reverted to his previous support for Turkey’s accession.)

Although Cameron tried to play down the prospects of Turkish membership, he deliberately avoided going as far as to offer the lock that Leave campaigners were asking for. According to accounts by those close to the Remain campaign, this was due to concerns about the wider impact that this would have on British-Turkish relations. In many ways, this is one of the big ‘what ifs’ of the campaign. What would have happened if Cameron had issued a statement that Turkish accession would be subject to a referendum?

As the campaign entered its final stretch, the question of immigration was clearly a key issue for many voters. Moreover, analysis by Martin Moore and Gordon Ramsay at King’s College London on the press coverage at the time has shown that Turkey, far more than any other country, dominated this debate. The next country in the list, Albania, did not come close in terms of mentions.

Ultimately, the claim that Turkey was on course to join the European Union, and that this would lead to an almost immediate surge of immigrants into Europe, and thus the United Kingdom, seems almost certain to have shaped the views of a significant number of voters. Whether this was merely an additional reason to leave – or was the issue that swung it – is hard to say. However, given the significance or the immigration debate and Turkey’s central role in that discussion, and given how close the final result was, there is a good case to be made that the unfounded claims made by the Leave campaign about Turkish membership of the EU have ultimately cost Britain its own membership of the Union.

This post represents the views of the author and not those of the Brexit blog, nor the LSE.

James Ker-Lindsay is Professor of Politics and Policy at St Mary’s University, Twickenham and Senior Research Fellow at LSEE-Research on South East Europe, European Institute, London School of Economics and Political Science. This post is based on his article in Turkish Studies (Volume 18, Number 1, 2018).