In 1945, when the British astonished even themselves with the "Labour Landslide", people knew at once that their world had changed course. In the cities, they flooded out of doors and in London the crowds sang "Land of Hope and Glory" - a choice which seems puzzling now but did not seem at all inappropriate then. Britain (or "England", as most of its inhabitants still called it) was obviously going to be mightier yet. The nation had thrown off chains and renewed its energy, to become a light of social justice and progress to the rest of the world.
And I can still remember the terror of the losers. The headmaster of my private boarding-school told us that, if Labour won, the high stone wall separating us from the village school next door would be torn down and a horde of ragged oicks would pour in to sack our dormitories and feast on our macaroni cheese. My grandfather, fearing a capital levy (which was never more than a hysterical rumour), sold off his collection of books and manuscripts for a knockdown price.
When Francois Mitterrand won in 1981 with the "Common Programme" of Socialists and Communists, Paris danced. With saxophones and songs, wine and hooting cars and open-air parties along the Left Bank, the Red Rose was saluted with red flags. It seemed then that the tradition running back through the Popular Front and the Commune to the Great Revolution, the France which had been kept out of power for nearly 50 years, had returned at last.
After the dancing, there is always a hangover. Labour under Clement Attlee could not live up to all its promises; Mitterrand soon dumped the Communists and moved from a socialist economic programme to something more like the policies of Reagan and Thatcher. But celebration itself, the moment at which private feeling becomes public, is important. It registers popular faith in the political process. It shows whether people are only abandoning a worn-out past or actively welcoming a future.
And these moments also stay with those who celebrated, memories - proud or bitter with hindsight - which help to decide how those people will vote or think for the rest of their lives. Sometimes it is hard to know how those memories will work. In Poland, the squabbling groups which dispute the legacy of Solidarity long ago lost the attention of most voters. And yet the memories of June 1989, that flooding-over of incredulous joy into partying as people realised that their votes for Solidarity had mortally wounded the Soviet system in Europe, are saved up and hoarded by everyone.
When Margaret Thatcher resigned in 1990, nobody quite expected that extraordinary, absolutely physical sense of relief. Millions of us experienced it - including, to their intense surprise, a great many Conservatives who had supposed themselves loyal to the Lady. It was in the shoulders, like a heavy rucksack falling off, and it was in the lungs, like the first great intake of mountain air after a long car journey. For myself, I felt lighter and fitter for days. That feeling wasn't to be predicted, and asking if we will dance in the streets when the Tories fall is asking a deep question about Britain's political subconscious.
Perhaps relief, rather than joy, is the key emotion. In this country, it is a long time since a political outcome brought public ecstasy. As the Englishwoman was supposed to say to her husband, "Feel better now, dear?" When John Major unexpectedly won the 1992 elections, the voters fell into a heavy, frustrated, undischarged mood. It is fairly clear why. People assumed that the Tories were going to lose, but in the polling booth a large minority of waverers secretly voted Conservative, supposing that everyone else would do the job of changing governments for them. When it turned out that they had put the Tories back yet again, they were quite disconcerted. With a part of their minds, they had already accepted a change of regime.
In some places, that fabulous night when the axe finally connects with the Tory neck will indeed bring delight. The Scots, in their large majority, have been voting against Conservative government for 18 years and the feeling about the Tory party today could be described as widespread hatred. There will be a party to remember in Edinburgh and Glasgow that night. And yet even there the emotions will be as much vengeful relief as joyous welcome to the future. Victory for Labour or a Lib-Lab alliance means the restoration of Scotland's parliament and the opening of a wide door to all kinds of national prospects. But it will also mean the end of a long affront, a savouring of revenge - which is always directed towards the past.
For most of the United Kingdom, the end of the Tory years will feel, at best, like emerging from a tunnel into unaccustomed light. Not for the Tories themselves, of course. Five years ago, it was possible to meet Conservatives - mostly of the One-Nation or Wet tendency - who would say privately that a period in opposition was what the party needed, in order to wash off the grime of too many years in power and restore unity. Now it is too late. The same people anticipate in opposition only a merciless internal shoot-out, which will probably end in the party's capture by the extreme nationalist Right.
Nobody expects a New Jerusalem from New Labour. Britain under Tony Blair may be necessary and inevitable, but it is hard to find much driving enthusiasm for it. I suspect that the early years of a Blair government will turn out to be more vigorous and interesting than we think, but Labour is carefully avoiding any Wilsonish promises to transform society in its first hundred days.
Even the scarred old constancy which made people vote Labour through thick and thin has faded. When I lived in Germany, and the opposition Social Democrats (SPD) used to agonise their supporters by one ghastly blunder after another, they joked: "Scheisse! Trotzdem, SPD!" ("Oh, shit! But we're SPD in spite of it!") That dogged hope is something that neither Labour nor the SPD can count on today. Instead, Labour in particular faces an electorate impatient to see the Tories out but with phenomenally low expectations about what Labour might achieve.
Disillusion with politics, the Thatcherite myth that all change results from external and uncontrollable economic forces, is only part of the story. Shame is an equally potent factor. Millions of people took the Thatcher shilling for nearly two decades, and used it to buy into a system whose values were greed, selfishness and the right of the strong to trample the weak. Now they do not like themselves very much. They will punish those who led them astray. But they are not inclined to love the party of the virtuous, who warned them at the time that there was more to life than the trough.
When the day of judgement comes for the Tories, these chastened citizens will not swarm to Trafalgar Square with champagne and funny hats. They will toast the result at home in front of the box. They will not dance. Instead they will open another pack of lager, and drink it silently and very fast.