England, said Disraeli, "does not love coalitions". He should have known better. In 1874, he led a ragbag coalition, called the Tories, to election victory and government. "Broad church" is Labour's euphemism for loose alliances, held together by political convenience. Yet, despite possessing neither defining ideology nor homogeneous membership, the two British parties that can reasonably aspire to power are passionately opposed to sharing it with anyone who claims a different allegiance. Their prejudice has become conventional wisdom. Discussions of the Conservatives' capricious opinion poll lead nearly always end with agreement that good government depends on one party winning an overall majority. A "hung parliament" - with ministers living from day to day - would certainly be a disaster. But that is not the only alternative to landslide victory. That is cause for rejoicing. The days of majority government are probably over.
When Labour lost its overall majority in 1976, 67 MPs were from "minority parties". Today, there are 94. After the general election next year, there could be many more. We live in an age of political fragmentation.
Next year, because of disillusionment with the conduct of the present parliament, there may be MPs from the wilder shores of politics - Ukip and BNP - and "independents" with no policy except obedience to the wishes of the constituencies they represent. Forming a viable government could well require negotiations with Esther Rantzen, Martin Bell and Terry Waite as well as Nick Clegg. Whips will console themselves with the thought that the opposition is hopelessly divided. But, at a time when unpopular decisions are essential, ministers will live in fear that as soon as they face hard facts their enemies will all unite to turn them out.
A role for the Lib Dems
The ad hoc arrangement between Labour and the Liberals worked between 1976 and 1979 because David Steel, the Liberal leader, believed that the national interest required a period of stability. But he could not have guaranteed the government two years in office if the idea of a Lib-Lab pact had been proposed at the beginning of a new parliament.
Clegg, when speculating about a hung parliament after the 2010 May election, announced recently that he would give his support to whichever party "wins" - though he was not clear if, when the time came, he would count votes or seats as proof of victory. His decision, which amounts to a denial of the Liberal Democrats' independent existence, would be based on arithmetic, not policies or principles. So one possibility is a minority Tory government, which is antagonistic to European integration, committed to increasing the inheritance-tax threshold to £1m - and yet is propped up by Liberal Democrat MPs.
Whichever party won most seats, Lib Dems with ideas of their own would not tolerate such a subservient role. Some of them have already made that clear. So, were the situation to arise, there would be an à la carte arrangement, with all the damaging uncertainties against which the Institute for Government warned in its recent report, Making Minority Government Work.
Clegg's plan for making the Lib Dems an unstable extension of another party confirms that the creation of a proper coalition - a negotiated partnership based on common values - is a more attractive proposition than Disraeli realised. It ought to be particularly attractive to genuine social democrats - not because Labour may lose next year, but because the party will never fight a general election on radical policies as long as it feels that it must struggle to win an overall majority. Total victory requires success in the marginal constituencies in the suburbs of southern England. It was on their behalf that Labour reduced the basic rate of income tax from 23 pence to 22 pence and abolished the 10 pence rate to fill the revenue gap.
In its attempt to be all things to all voters, Labour lost its moral impetus. It can only regain it by becoming an openly egalitarian party which accepts that its aim is to become the largest single party in the House of Commons and then lead a radical coalition. The ingredients are already there.
Can old friends reunite?
Plaid Cymru and the Scottish Nationalists owe more of their popularity to filling the space that Labour has deserted than to an enthusiasm to break up the UK. And the Lib Dems themselves - admittedly with a leader who looks like a polystyrene replica of David Cameron - contain members who are clearly and openly radical. It is absurd for the Labour Party to treat Vince Cable and Shirley Williams as enemies. They are, by instinct and intellect, better social democrats than half of Tony Blair's old cabinet. Labour's immediate task is to appeal to its natural allies - leaders and led.
Under the present electoral system, neither major party can openly prepare for anything except outright victory. To admit the possibility that a coalition might be necessary is to concede defeat.
But the present system will not endure. Proportional representation is irresistible. I now welcome the change, not because what is called "electoral reform" is more democratic than "first past the post". The slogan "Fair votes" is a fraud. But PR makes coalition certain and liberates Labour from the hope of winning 326 or more parliamentary seats.
Under a new system, a return to principle will follow. So will the radical coalition that was tragically destroyed when Liberals and Labour went their separate ways 90 years ago.
Roy Hattersley's most recent book is "In Search of England" (Little, Brown, £18.99)