The past is an unreliable guide. No one knows what will happen next, and looking back for a route map is treacherous. There is, though, a significant exception to this rule. Britain's only national referendum, held in 1975, provides important lessons as leading players contemplate a second national plebiscite next May. The stakes could not be higher. Already the referendum on electoral reform is seen as a defining moment for the coalition and to some extent for Labour too. For once we can head backwards with confidence to discover what the future holds.
There are many parallels. A Labour government that had failed to secure an overall majority called a referendum in 1975 on whether or not Britain should remain in the Common Market. The campaign took place against the backdrop of the Treasury preparing substantial cuts in public spending, reductions that the Chancellor at the time, Denis Healey, later admitted were based on unnecessarily pessimistic assumptions.
As with the one planned for next year, the referendum in 1975 was called as an act of expediency, not because the Prime Minister or his colleagues had discovered a sudden interest in direct democracy. The Cabinet and the rest of the Labour Party were split on Europe. For the Prime Minister, Harold Wilson, the referendum was a device to keep the fragile show on the road. David Cameron offered a referendum on the Alternative Vote to Nick Clegg in order to get the show started.
The current Cabinet is split along similar lines to Labour's in 1975, with several ministers feeling passionate on either side of the argument and quite a few not feeling so strongly but veering towards maintaining the status quo.
Cameron is in the latter group, as Wilson was. He will campaign for a "No" vote and has genuine doubts about a change to the Alternative Vote. He has been known to reflect that if AV had been in place in 1997 the Conservatives would have been virtually wiped out, as Labour might have been in 1983. Cameron plans to make a few speeches during the campaign, but emphatically will not be a leading figure.
This is partly because as Prime Minister and leader of the coalition he will have to deal with the consequences of the vote either way. He is ready to do so. If there is a vote in favour of a change, he will not be too perturbed. He has pointed out to fiercer opponents that AV is not a form of proportional representation and retains the constituency link. He is adamant that he would never have granted a referendum on PR.
And yet, as he plans to campaign in a subdued way for the status quo, Cameron wonders, sometimes aloud, whether he is leading an historic realignment of the centre and centre-right, one that might be cemented by a change in the voting system. He campaigns for one outcome and is ready to respond to another.
In 1975 Wilson led a coalition even though it was formed from a single party. The gap between Tony Benn and Roy Jenkins, two senior ministers, was much wider than that between Cameron and Clegg. Although he was Prime Minister, Wilson did not play a prominent role in the campaign. He made two speeches in favour of a "Yes" vote and that was it. The stars of the "Yes" campaign were Jenkins, the recently ousted Tory leader, Ted Heath and the Liberal leader, Jeremy Thorpe. The new Leader of the Opposition, Margaret Thatcher, also campaigned actively for a "Yes" vote.
Wilson wanted a vote in favour of the status quo, but was not especially passionate as he was already becoming disillusioned with the demands of European membership. His overwhelming passion was to keep his government and party united once the referendum was held.
During the 1975 campaign Wilson granted his Cabinet what he called an "agreement to differ". As they differed with such intensity he had no choice. Cameron will do the same. The most memorable consequence in 1975 was a live Panorama on BBC1, in which Jenkins and Benn clashed for 50 minutes. As a young teenager I found it as exciting as a Sex Pistols' concert. Jenkins said that he could not take Benn seriously as an economics minister. With mesmerising charm and wit Benn challenged Jenkins's claims about Europe's democratic mandate, arguing that Brussels would block Labour's plans for the economy. Viewers were left with a sense that things would never be quite the same again in the Labour Party.
What followed the easy win for the "Yes" campaign in 1975 was highly significant. In the short term at least the prominent losers suffered. Wilson felt emboldened to demote Benn, moving him away from the Department of Industry to the much less influential Energy portfolio. Soon afterwards Wilson's successor, Jim Callaghan, sacked Barbara Castle from the Cabinet. Castle had been another star of the "No" campaign. More widely, for a few years Wilson's device worked. Europe faded as an issue. The Cabinet survived until 1979.
But after Labour's defeat the issue erupted again. By the 1983 election Labour was pledged to withdraw from Europe without the offer of a referendum and several of its former Cabinet ministers had left to form the pro-European SDP.
Given the parallel, here is what we can expect when the referendum is staged next May. Cameron will handle the immediate campaign with ease. There is no reason why he should lead the "No" campaign. There were no calls for Wilson to head the "Yes" onslaught in 1975. Whatever the result the coalition will not fall in the immediate aftermath. Each side will have had its chance to put a case. The opportunity is the unifying device. The result is in the hands of the electorate.
Nonetheless, leading players on the losing side will suffer a substantial loss of authority. Wilson could never have demoted Benn if the "No" vote had won in 1975. The coalition will continue but it will no longer be seen as a partnership of near equals. One group of ministers will have won a national poll and another will have lost. The dynamics will change.
The outcome will impact on the new Labour leader too. As was nearly always the case in her early years, Thatcher judged the mood perfectly in 1975. Whatever form her embryonic Euro-scepticism was taking she backed the winning side. If she had campaigned for the losers she might not have recovered. The AV referendum poses a bigger challenge to the new Labour leader than it does to Cameron.
At least it does in the short term. In the longer term the lesson of 1975 is that referendums do not kill off an issue or the politics that surround it. The Jenkins/Benn clash did portend a fatal split for Labour, but the schism was postponed for five years. Europe has never gone away as a divisive policy area. At some point the pluralists in the coalition will clash fatally with the tribalists, but that point might be several years away. Whatever the result, voting reform will not die. If AV is won, there will be calls in five years' time for proportional representation. If it is lost, expect calls for a re-run before very long. Once more nothing will be quite the same again, the final lesson from 1975. Referendums are not cathartic but lead to a tidal wave that threatens innocent participants for years to come.
For further reading
'Harold Wilson', by Ben Pimlott (Harper Collins, 1992); 'Against the Tide: Diaries, 1973-6', by Tony Benn (Arrow, 1990)