It is 40 years exactly since Downs, an American political scientist, predicted that the main parties would shift ever closer together in their eagerness to win each other's voters. Then, he said, the people left standing on the fringes of politics would become alienated and minority parties would spring up to serve them.
With Labour and the Conservatives apparently at one on crime, educational standards and the market economy, could it be that the growing band on the margins are fighting back?
After all, the argument goes, this is what happens when neither main political party wants to discuss abortion. Voila! A brand new party with 50-plus candidates, all eager to talk endlessly about their pro-life views. Little mileage for either Labour or Conservatives on Europe? Not one group but two, boasting almost 800 candidates between them so far. But the prospects for these factions are not good. Patrick Dunleavy, professor of government at the London School of Economics, explains: "They will get no recognition and everybody will make fun of them. Then they will lapse again."
Do you remember, for example, the Natural Law Party? The Islamic Party? And the Green Party, which could command about 15 per cent of the vote in 1989, is now running at around 4 per cent in the polls.
Downs would have us believe that we have already reached our final destination. That the future political scene will consist of two identical beacons, surrounded by a host of moths which constantly crash and burn in their flames. After all, even the Liberal Democrats are seeing their vote squeezed.
But there is another view. Around the world, political systems are becoming more fragmented and people are choosing from a wider range of parties, according to Professor Dunleavy. It could happen here, too.
With the Conservative Party apparently ready to split over Europe, with the newly launched Socialist Party ready to woo the Old Left abandoned by Tony Blair, the voters could soon have four or five parties to choose from. Issues which sat uncomfortably in the old left-right spectrum could come to the fore: race, religion and gender could be just as important.
And with the possibility of proportional representation, the cycle of convergence, alienation, fragmentation and adjustment could be broken. Those small groups may not be so small in future - after all, a minority party is only a majority party that has failed to succeed.