Now, in the wake of Brexit and Corbyn, those old certainties are being smashed. Tribal voters are floating voters. Die-hard Tories and Labour loyalists are mulling over the prospect of playing away in the polling booth. These might seem like moves born of desperation; these times might cause many to despair, but take heart! In the long term, this disbanding of the tribes will have a powerful and positive effect on our democracy.

The notion of belonging to one political tribe or another goes back a long way. In Gilbert and Sullivan’s Iolanthe of 1881 it is observed “How Nature always does contrive . . ./ That every boy and every gal/ That’s born into the world alive/ Is either a little Liberal/ Or else a little Conservative!” In truth our political leaning is most often down to nurture more than nature; parents and postcodes decree whether a little Liberal or a little Conservative a child shall be. One friend in his seventies was asked to promise his late mother that he would never, ever vote Tory — a promise he has kept for 50 years.

For most of the 20th century the Conservative-Labour duopoly claimed the allegiance of a vast majority; in the 1960s eight in ten identified strongly with a political party. The great unravelling of these loyalties has accelerated in the past ten years, with only half the electorate voting the same way in 2010, 2015 and 2017. Half! Fifty per cent of us were prepared to shrug off our allegiance to a party in that short space of time.

At the last election there was no greater symbol of voter volatility than the swapping of Canterbury and Mansfield between Labour and the Tories. Canterbury had been Conservative since 1918; Mansfield, the former mining town in Nottinghamshire, elected its first Tory since the constituency was created in 1885. So unthinkable was this that the returning officer called a Labour victory by mistake.

In recent weeks we have seen party swapping on steroids. MPs defecting to the Lib Dems. The former Labour MP Ian Austin telling us not to vote Labour. The former Conservative cabinet ministers Ken Clarke and Justine Greening teasing that they may not vote for their own party. Tories having in their sights places such as Ashfield and Bolsover, seats that have long been red. No doubt we’ll have colliery bands playing at Boris Johnson’s rallies soon.

Together, two things that may be undesirable in the short term — national divisions over Brexit and Jeremy Corbyn’s disastrous leadership — are achieving something highly desirable in the long term. They are eroding the idea that your background, income, profession or age should mean you belong to a party for life. Thanks to Brexit’s furies and Labour’s fantasy economics, the bonds of political tribe are finally wearing away. How refreshing this is, and how long overdue, for when political parties feel they “own” blocs of voters, unhealthy things happen.

First, the party feels it must cater to its own tribe to keep them sweet, regardless of whether these bungs or policies are in the national interest. We see this in Labour’s obsession with identity politics, mimicking the outrage of some of its supporters on the latest trivial battle in the culture war, or (when they were in government) in their pork-barrel bungs to parts of the north and Scotland. We see it too in the Conservatives’ endless courting of older voters, and in their refusal to confront nimbys in the battle to build new homes for the younger generation.

Perhaps more damagingly, when parties feel there is a section of the electorate who will always put an X in their box (the above rule having been observed), policy innovation is put on the back burner. If a town contained only a Waitrose and a Tesco, and its inhabitants had taken a blood oath only to shop at one or the other, there would be no burning incentive for either to improve its products, cut prices, offer free coffees and parking. Tribal politics kills the fierce, genuine competition that is the mother of invention.

So the dwindling of tribal allegiance should mean, in time, the flourishing of new ideas. Once less bound by what their core vote might feel, parties will be able to think with the safety catch off, prioritising what works rather than whether it will play well with their base. We might describe the process we are undergoing as the move from “contract voters” to “consumer voters”. In the old, tribal politics, loyal voters had a contract with their party of choice: you scratch my back with the policies and tax cuts I expect, I’ll scratch yours by dutifully heading down to the polling booth come election day.

In the new, party-swapping politics, elections will become a vibrant buyers’ market, with many more completely unaffiliated voters free to shop around for the policies they like best. Manifestos might even get read.

Consumer voters will have a powerful effect not only on the ideas being offered but the people, too. Many would agree that the quality of MPs in parliament today is not uniformly brilliant — but the end of tribal politics should help change that. With fewer people automatically voting for a party they have inherited from their parents, there will be fewer safe seats in which the proverbial donkey in the red or blue rosette wins. Parties will have to up their game on getting truly outstanding candidates to stand for election, because when the colour of the rosette matters less, the calibre of the candidate will matter more. They will be scrutinised not only as a member of the red, blue or yellow team but as an individual — so we can expect the quality of MPs to improve, too.