"Who governs Britain?" Aspiring barristers are taught that you should never ask a question in court to which you don't know the answer. Edward Heath forgot that rule in February 1974 when, after months of industrial turmoil culminating in the three-day week, he called an election and, by way of challenging the unions, asked that question.
And the electorate replied: Not you, chum. Or at least, so far from being returned to power with a healthy majority, Heath found that he had no majority at all. On St David's Day, the day after the election, the fun and games began.
The story of Friday 1 March 1974 is riveting enough anyway, but might soon become acutely relevant. It is quite possible that on the morning of Friday 7 May 2010 - which will probably be the day after our next general election - David Cameron and the Tories will find themselves with a plurality, or more seats than any other party, but without an absolute majority over all others: in the modern jargon, a hung parliament.
When the final results were tallied in March 1974, the Tories had 297 seats to Labour's 301, some way short of the 318 needed in a Commons of 635. The long-awaited Liberal revival had begun at last, while the Union was fragmenting. In 1955, the Tories had won almost half the popular vote and 365 seats out of 630, not least with what now seems barely believable - a majority of seats in Scotland; and these 365 included the "UUs", the ten Ulster Unionists, who voted supinely with the Tories.
In 1974, the two larger parties each won less than 38 per cent of the vote; there were 14 Liberals, seven Scot Nats and two Plaid Cymru, while with the Paisleyite insurgency, much of "loyal" Ulster had deserted the Tories. And so Heath began to look for ways of retaining office by cutting deals. On the Friday, he summoned Jeremy Thorpe, the Liberal leader, for a two-hour meeting at Downing Street to see on what terms the Liberals might support a continued Tory government.
A cabinet post, which both men assumed would be home secretary, was dangled in front of Thorpe, who wanted to accept but said that he would have to consult his party. The party turned out to be highly displeased with these personal intrigues, and had a sticking point: it would only support another party in return for the holy grail of proportional representation.
There was a twist in the story that no Michael Dobbs or Robert Harris would have dared invent. Thorpe was being harassed by Norman Scott, a former boyfriend. In October 1975, Scott was threatened by an armed man who shot his dog; then, in 1978, Thorpe was prosecuted for conspiracy to murder. It defies any novelist's imagination to suppose what would have happened if, as the secretary of state responsible for law enforcement, he had been investigated on such a charge.
That lurid subplot aside, Labour announced that it was "prepared to form a government and submit its programme for the endorsement of parliament"; Wilson wanted to denounce Heath's supposedly unconstitutional behaviour: his secretary Marcia Williams said it was "as if the referee had blown the whistle and one side had refused to leave the field". Fortunately, James Callaghan and Roy Jenkins dissuaded Wilson from saying something that would have been not only tactically inept, but simply wrong.
The classical doctrine is that "we have a government" until it has been defeated in parliament, or has voluntarily resigned. Heath was entitled to stay in Downing Street until it became clear he could not form a workable majority. And that was what happened on the following Monday. Whatever his own wistful yearnings, Thorpe was obliged by his colleagues to write to Heath: "I do not believe that a Liberal presence in the cabinet, designed to sustain your government, would be acceptable." By late afternoon Sir Martin Charteris, the Queen's private secretary, rang to say: "Would it be convenient, Marcia, for Harold Wilson to be at the Palace at 7pm?"
In turn, the minority government that Wilson now formed was awkwardly placed. A little more than six months later he asked for a dissolution, and in October Labour won, but with an absolute majority of just one seat.
There were endless troubles ahead as that majority evaporated, and in the end Margaret Thatcher's motion of no confidence brought down the government and precipitated the 1979 election, which left Labour out in the cold for 18 years.
And yet the rarity of that event - the first time a government had fallen on a Commons vote since 1924 - only illustrates how much times have changed. So does the very phrase "hung parliament", an American import taken from "hung jury". The expression is un-English, and it is a concept that made little sense for much of our history. Until the 19th century, the idea of a parliamentary majority barely existed. Most MPs were silent and inert, even when they bothered to appear at Westminster, while prime ministers ruled by a mixture of persuasion, patronage and simple corruption.
After the Reform Bill of 1832, the balance changed in a quite unforeseen way and there was a long period of political turbulence, with party allegiance loose and ill-disciplined. In the wake of a general election, no one was ever quite sure how many MPs counted with which party, and sometimes it was not clear who could form a ministry.
Minority governments - in "hung parliaments" - were almost as much rule as exception throughout Victoria's reign, while governments were made and unmade by parliament with almost frivolous ease. After an election, a prime minister in office might well wait until parliament met and only resign once defeated in the Commons, which is one reason why every government between 1837 and 1874 fell following a Commons vote.
Political and parliamentary life was all manoeuvres, tactical gambits, resignations and ambushes. In December 1852, William Gladstone rose to speak to a crowded Commons well after midnight, eloquently demolished the Budget the then chancellor, Benjamin Disraeli, had just presented, and brought down the government. In 1873, by which time they were leading their parties and Gladstone was prime minister, "Dizzy" had his revenge. Gladstone's first government had run out of steam and was beset by scandals. Rather than call an election. Gladstone resigned, challenging Disraeli to form a minority government. But Disraeli was too sharp, saw a trap and declined to accept office, the last occasion this has happened.
After the dramas of the 1880s and the failure of the First Home Rule Bill, the Tories were in power from 1886-1905 with only the Liberal interlude of three years in 1892-95. In 1892 the Liberals won 273 seats to 269 Tories, with 46 Liberal Unionists, 81 Irish nationalists, and a solitary independent Labour MP. Neither of the larger parties had anything near the 336 needed for an absolute majority, but Gladstone, in his eighties, was determined to find a settlement for Ireland, and did pass the Second Home Rule Bill in the Commons before the Lords threw it out. Then, under Rosebery, his successor as premier, the government was defeated on a snap parliamentary vote; Rosebery resigned, and easily lost the ensuing election.
At the end of 1905, the Tory government under A J Balfour was demoralised and divided. Although Balfour still had a clear parliamentary majority, he resigned and challenged Sir Henry Campbell-Bannerman, the Liberal leader, to take over. Unlike Disraeli, "C-B" accepted the challenge, asked for a dissolution, and won a landslide in early 1906, which is why the last Liberal government in our history dates from 8 December 1905 (an episode of which Andrew Marr is apparently unaware, to judge from his new TV series, The Making of Modern Britain). Twice in the past century, there have been two elections in the same year, and both produced "hung" minority governments. Before 1974 it was 1910, when a first election gave the Liberals 275 to 273 Tories, with 82 Irish and 40 MPs from what was by then formally the Labour Party.
In an attempt to break the deadlock, H H Asquith called another election in December, but the result was almost identical, 272 each for the Liberals and the Tories, 84 Irish, 42 Labour. Although the Tories won a significantly larger share of the popular vote than the Liberals in both elections of 1910, they had campaigned almost entirely on opposition to Home Rule, for which there was a clear Commons majority. The Third Bill was passed only after a ferocious constitutional crisis and near civil war.
Over the ensuing decades, the Liberals declined and Labour rose, so that Labour was able to take office twice before 1930. But this was during the last period when we really had three-party politics, and the first and second Labour governments existed on sufferance. The election of December 1923 produced 258 Tories, 191 Labour and 159 Liberals, when 308 was needed for a majority.
While this was a defeat for Stanley Baldwin, the Conservative prime minister who had called the election, it was not a victory for either of the other two parties. As in 1974 - and maybe at next year's general election - the Liberals had to decide whom to support, and Baldwin had to decide what to do. He wanted at first to resign, but instead faced the music when parliament met. On 21 January 1924 he was defeated on a Labour amendment after the King's Speech. There was much talk of a Tory-Liberal coalition, and Beatrice Webb, surprisingly enough, thought that this would be "the honest" answer, which "would be approved by the majority of the British people". But then she always insisted that, for socialists like herself, "the real enemies are the Liberals". So much for the idea of an artificial split on the "progressive side" that Tony Blair and his minions used to lament.
Despite what proved well-founded warnings from Labour colleagues, Ramsay MacDonald accepted the king's invitation to form a government, which quickly came to grief. After some months of passive support for MacDonald, the Liberals joined the Tories in voting against the government in October, precipitating the third general election within two years.
In 1929 MacDonald was back, but this was in another minority government - Labour 288 MPs, 260 Tories, 59 Liberals, in a Commons of 615 MPs - which collapsed in the lurid circumstances of the 1931 financial crisis.
What all this teaches is that the Tories could form a government in May, even if they don't reach the elusive 326 needed for an absolute majority in a Commons slightly larger than at present, perhaps by making the Lib Dems an offer. The idea of Vince Cable as chancellor is beguiling, and why not Sir Menzies Campbell as foreign secretary, to reward his well-informed criticism of the Iraq war?
Or possibly Labour could offer the deal the Lib Dems thought they had in 1997, until Paddy Ashdown found what a promise from Tony Blair was worth. One way or another, it could be an exciting as well as a merry month of May.
Geoffrey Wheatcroft's books include "The Strange Death of Tory England" and "Yo, Blair!"