As we survey the aftermath of Jeremy Corbyn’s election as Labour leader, an outcome bookies would have offered 100 to 1 on just a few months ago, it’s worth considering the mere 2 to 1 shot (Ladbrokes) that Britain votes to leave the EU before the end of 2017.

The last vote on the issue was in 1975. Several commentators have pointed out the parallels between that referendum and today’s, but more important than what is similar is what is completely different. There have been four key areas of change, all of which, in my view, have increased the chances of Brexit.

The first is the change to the European Union itself. In the last forty years there have been five major treaty amendments, two name changes and 19 new members. The introduction of Free Movement, the formation of the Eurozone, the trauma of Maastricht and the ignominious exit from the European Exchange Rate Mechanism (ERM) have all occurred in the intervening period. Now, new voting rules have raised the prospect of a “tyranny of the qualified majority”, in which the EU is gerrymandered to the interests of the Eurozone whilst the UK agenda is side-lined. What in 1975 was presented as a trade bloc stands today as an increasingly integrated political project, to the dismay of many voters.

The second change is the link between immigration and EU membership. This is encapsulated in the first point, but took on a life of its own following the eastward expansion of the EU in 2004. Today immigration leads voters’ list of concerns, ahead of the economy and the NHS, with 45 per cent naming it among the “important issues facing Britain”. The current refugee and border control crisis looks likely to reinforce existing concerns. And while not all eurosceptics are opposed to immigration (Douglas Carswell springs to mind) it is likely that the ability to “regain control of Britain’s borders” will form a key plank of the Leave campaign.

Of course, even in the event of Brexit it is questionable whether Britain could place strict limits on EU migration without risking its access to EU markets - Non-EU member Switzerland has been faced with just such a dilemma. But whether such nuances will cut through in the campaign is another matter. Much will depend on the press, which brings us to the third change: the British press is far more eurosceptic now than it was in 1975.

It seems strange to imagine the Daily Express or Daily Mail exhorting their readers to vote in favour of EU membership, but at the last referendum, all national newspapers, with the exception of the Communist-supporting Morning Star, joined the pro-European consensus. Today of course, things look very different. The Express and Star newspapers will almost certainly campaign to leave. The Mail, Telegraph and Rupert Murdoch’s Sun, Britain’s most popular paper, could potentially join them. In an era of declining readerships and online news outlets the positions of the press may seem less important. But most online traffic still goes to the major newspapers and UK impartiality rules allow newspapers to punch above their weight, as the positions they take become news fodder for the broadcasters.

The fourth change is the relative health of the UK economy. The 1975 referendum took place against the backdrop of the UK’s second consecutive year of recession. British commentators looked enviously across the Channel, one Times editorial reading “How much better off Britain would be if we had followed the same disciplines on inflation as Germany throughout, or more recently France”. The sense that, in Europe, Britain had found a potential solution to its endemic structural problems was pervasive. Now, as much of Europe lies in stagnant repose, punctuated by the occasional political convulsion, UK growth chugs along at an annual rate of 2.8 per cent. The risk of “going it alone”, if you believe it exists, is not the looming shadow it was in 1975.

Adding to these factors is the apparently negligible willingness among other EU member states to make concessions to the UK agenda. David Cameron has shelved hopes to win concessions on free movement and looks likely to have to abandon plans to limit in-work benefits for foreign EU nationals too. As a negotiating strategy it might be summed up in a phrase familiar to early users of Facebook: taking what we can get. Wilson’s negotiations achieved little as well of course, but in the absence of press criticism (a typical Times headline reading simply, “Wilson lists his achievements”) they were presented to the public as an unqualified triumph. It was left to historians to provide a withering verdict: “an enormously hollow exercise in political spin” in the words of Dominic Sandbrook. David Cameron is unlikely to have to wait for the verdict of history for similar criticism.