So what had the elections of 1964, 1966, 1970, February 1974 and October 1974 really decided (apart from the procession of removal vans ferrying the belongings of defeated prime ministers from Downing Street)? In an important edition published in 1981 and co-edited by Butler under the title Democracy at the Polls, a highly original chapter by Anthony King asked, “What do elections decide?” As it turns out, the question was more searching than the usual concern of journalists and psephologists alike: “What decides elections?”

King’s question is relevant for all elections but particularly so for Britain’s forthcoming vote on June 8. If the room for manoeuvre was so limited for British governments in the 1960s and ’70s, will the new administration be any freer in its dealings with EU negotiators about the terms of Britain’s leaving? Will the choices for UK voters turn out to be so unsatisfactory that, in one way or another, the country will once more be forced to grovel and to obey rules of the game imposed in Brussels and Berlin? If so, will this year’s general election, like so many earlier ones, have been of no lasting significance?

The answer is that electoral outcomes, while usually constrained by economic and geopolitical realities as well as what Macmillan called “Events, dear boy, events,” may matter a lot but only very occasionally. Possibly the only general elections which have had deep consequences since the Second World War were those of 1945, after which Clement Attlee’s Labour government created a social democratic mixed economy, and of 1979, when Margaret Thatcher used her victory to curb its dangerous extravagance. Even Mrs Thatcher felt constrained in challenging senior cabinet colleagues who were prepared to go along with the European project of “ever closer union”. Tony Blair’s landslide in 1997 was possibly more important for the constitutional changes introduced under his premiership (which were of relatively little interest to him) than for his actions concerning economic and foreign affairs.

Whatever the constraints on democratically-elected British governments of recent decades, they do not compare with those which would have existed in the future under the terms of the Lisbon Treaty had the 2016 referendum had a different outcome. Having already been obliged to confront the relatively weak European Court of Human Rights in Strasbourg, Theresa May has rightly been deeply alarmed by the prospects of rule by the far more powerful Court of Justice of the European Union in Luxembourg. The adoption of a vague, expansive Charter of Fundamental Rights has given the Luxembourg court a legal sledgehammer with which to batter the House of Commons.

Very powerful forces will be at work to constrain Britain’s negotiators. EU bureaucrats will be skilled, probably devious. After his time in 2015 as Greece’s finance minister, the warnings of Yanis Varoufakis need to be taken very seriously indeed. My own experience at the outer margins of Euro-negotiations, especially during the work of the UK Commission on a Bill of Rights, has impressed me with the huge influence of procedure: physical placements around a table, timetables of meetings, agendas, preparation of documents, minutes, simple tactics of divide and rule of the “enemy” and, especially, closeted settings and artificial decision deadlines. These are well-known tactics. Yet, I was very struck by how effective they are in breaking the will of highly-skilled professionals. At first, it may not appear necessary or reasonable to risk an early fracture by resisting points of procedure. But beware. And take account of recent European history.