This is the election of a lifetime – don’t miss your chance to vote in it

It has been said that the British general election of 2019 is a “once in a generation” affair. It is true, and it is why it is so crucial to register to vote and then to exercise that right.

Brexit alone makes it a crucial one for the biggest social, economic and constitutional change since the UK entered the then European Community in 1973. Beyond that, there is one of the starkest of choices ever placed before the voters.

A radical-left populist Labour Party is faced by a radical-right populist Conservative Party. Opinions are polarising so much that the Liberal Democrats are being badly squeezed out, the last thing that might have been expected to occur when the fabled “centre-ground” of politics has been left abandoned. In Scotland and Wales, people are looking to nationalists for answers. The Greens and the Brexit Party are being out-competed by their supposedly more mainstream rivals.

There is, then, a lot at stake. Which is why the voters who have managed to register (a process that takes only a few minutes online) and fulfilled their legal responsibilities also have a moral duty to turn up and vote on 12 December. The worst feeling would be to wake up on Friday the 13th and face a Nightmare on Downing Street – whether that is the apparition of Boris Johnson or Jeremy Corbyn or, just possibly, some other figure, waving in front of the famous black door.

Whatever the parliamentary arithmetic comes to, someone will have to form and lead some sort of government. And the policies followed by a Labour or Conservative government, either as minority or majority administrations, will be as revolutionary as anything we have seen since the 1980s. A vast experiment with Brexit, or with state socialism, or both awaits the country. It would be better for most people if they had at least participated in the process of getting there, whether to consent or object to it.

Of course, under the British first-past-the-post system, not every vote is equal. General elections are traditionally won or lost in a relatively few marginal constituencies. For many decades they have been concentrated in the midlands and the north of England, and this is still the case. Yet new patterns of voting and different political structures have also emerged. Although the 2017 election saw some return to two-party politics, and the present campaign seems to be following that same course, the emergence of the SNP in Scotland, and to a lesser extent, Plaid Cymru in Wales have left those nations with very different choices.

The arrival of Ukip, the on-off revival of the Liberal Democrats and the occasional flash of life from the Brexit Party have also been felt. In coastal communities on the east of England, for example, the Brexit Party could make a difference in some seats, as they did in the European elections.

In London, parts of the south and university cities, the Liberal Democrats are taking on the role of chief challengers to Labour. Seats such as Dominic Raab’s and John Redwood’s, in Esher and Walton and Wokingham respectively, are prey to the Liberal Democrats simply because their MPs are so out of sympathy with the residents’ Remain wishes.

By contrast, the Conservatives hope to pick up seats in new territories, such as Wales, Stoke-on-Trent and Wolverhampton, that have long been strangers to Conservatism. Denis Skinner, at 87, may be humiliated in Bolsover.

There are now new types of marginal seat, populated by new kinds of voters – ones who demand and exercise more freedom of choice, and are less bound by tribal habits. In Northern Ireland, the unionists could lose the historic stronghold of Belfast East. We also have more credible independents standing than in the past – from David Gauke and Anna Soubry to Frank Field. Then again, places such as Liverpool are becoming ever-more solidly one-party states for Labour. The nation is fragmenting politically more than at any time since the Labour Party began to displace the Liberals in the 1920s.

In many places, in other words, who votes for whom is more important than it has been for decades, such is the variety of contests and the opportunity for tactical voting and tactical campaigning (so-called Remain and Leave alliances) to make a difference. So every vote can count in some seats; and even where it might not, it is part of a national verdict on each party in any case, the key to their ability to claim a mandate for their policies.

We know too, indeed, how far Brexit has shaken old ways and provoked new divisions. Given the Conservative lead in most polls, it looks as though they may be the largest party in parliament – but that is far from inevitable, and a hung parliament is still a perfectly plausible outcome.

Every seat will count in such a scenario. Never before has someone born in the 21st century been eligible to vote. For them, just as for someone, who, at the then minimum franchise age of 21, first visited a polling station in 1945 to choose between Clem Attlee and Winston Churchill, it is just as vital and exciting a democratic act. Serious an obligation as it is, rattling the old political kaleidoscope can be a liberating, empowering, even fun thing to do.