The last year feels as if it has lasted for a decade. At the start of 2017, the Conservatives were riding high, and Labour was in the doldrums. Now, a reversal of fortune has switched the whole feel of British politics. It’s Labour, now, which feels the wind at its back – and the Conservatives that seemed dazed by the speed of events. Back in January, the Conservative lead as measured by pollsters was somewhere in between eight and 17 percentage points. At time of writing in late December, Labour leads, albeit by a slender 1.6 points (41 per cent to 39.4 per cent) if we take an average of the last results from all pollsters in the field.

Circumstances seem to be against the Conservatives. Every year around or about 700,000 young people turn 18 and gain the right to vote: looking at voting intention figures by age, that amounts to a lot of new Labour voters by 2022. Real wages are still falling, and they seem likely to go on stagnating. Brexit itself is likely to divide the Tories for many years to come. Will Eurosceptics really accept the Community’s entire acquis, or body of laws, for the whole length of a transition phase that looks likely to last in practice far longer than two years? It seems unlikely – and if and when their patience snaps, renewed Conservative civil war could be the result.

Conventional wisdom, therefore, holds that the next election is Labour’s to lose. That’s a good place to pause. Remember the conventional wisdom in January 2017? Yes, it held that Labour was heading for a big, and perhaps catastrophic, defeat. Conventional wisdom was wrong and it could be wrong again. The American pollster Nate Silver was very clear when he warned – weeks before the general election – that the snap election was a much riskier gamble than it appeared.

Looking back, polling experts might have noticed two things about all those very high Conservative leads. There is an idea that “the Tories usually outperform their polls”. Yet in a majority of postwar elections, they have actually underperformed their survey scores when they went into an election campaign ahead.

Second, Labour’s vote was being pushed, not just over to the Conservatives, but towards “don’t know” and smaller parties – the Liberal Democrats, for instance. Once Labour’s campaign showed strong signs of life, past partisanship and anti-Tory tactical voting took hold where once left-wing voters had been predisposed to register a protest, or perhaps not to vote at all.

Not everything is trending in Labour’s direction. The party is struggling to break away. That doesn’t mean it can’t or won’t, and indeed if you asked me this minute I would say that Labour’s lead will expand in the year or two to come. But there’s little evidence of that for now. Since the fevered period just after the general election when anything seemed possible, it has not at any point been able to establish a lead of more than two or three points on average. That should already have begun to worry Labour. For all the government’s travails, from the many ministerial resignations to the Prime Minister’s disastrous conference speech, it cannot press home its advantage.

The impression of stalemate is backed up by everything else we know. Council by-elections, albeit attracting only small turnouts, show on average only that movement that we would expect. Leader ratings as “best Prime Minister” consistently give Theresa May the lead over Labour leader Jeremy Corbyn, though that advantage is almost always in the middling single figures. That shouldn’t give the Conservatives all that much succour, for Prime Ministers usually look more “Prime Ministerial” than their rivals chiefly just by occupying the office. They often enjoy leads over the Leader of the Opposition, but that doesn’t always save them. Labour Prime Minister Jim Callaghan enjoyed a lead of up to 19 points with Ipsos Mori during the 1979 general election; he still lost.

So what signs of the unexpected should we be on the lookout for this time? Well, obviously in 2018 we will be looking to see if one of the two main parties can break the stalemate. Can Labour finally shake off the Conservatives, and establish a really strong polling lead – as it did when heading back to office in the early 1960s or mid-1990s? Or can the Conservatives, perhaps helped by some much-needed progress in Brexit talks and maybe some fresh faces and policies, eke out any sort of sustained lead?

Those are, however, just the headlines. Under the surface, one thing to look at will be how the two parties are doing in the marginals. This matters when we come to look at the balance of power in the House of Commons. The pollsters ICM have been running an (admittedly small sample) series of numbers on this in their usual voting intention polls. At the moment, the Conservatives enjoy a much smaller lead in their English and Welsh marginals than Labour do (though if we went by these figures alone, the numbers would mean the blue team losing only a handful of seats). Labour appears to be consolidating its grip on white-collar and middle-income voters in suburbs and larger towns. If that trend goes into reverse, it might first show up here.

Another element to watch will be the Liberal Democrats. On paper, you could not invent a better situation for them. With the Conservatives doubling down as the party of insular cultural nationalism, and with Labour led by a long-time Marxist, the party of the militantly sensible should be flying high. Instead, they are flatlining. Labour has completely cannibalised the Liberal Democrats’ reputation for radical, different, difficult oppositionalism. However, if the Liberal Democrats start to climb, perhaps under refreshed leadership later in this Parliament, that could shift the balance of odds gradually against Labour again.

One could add lots of other known unknowns. What, for instance, about turnout? Most pollsters have now adjusted their presumptions to take account of last time’s relatively high youth vote. Any fraying of that enthusiasm, or signs that turnout among older voters could rise again, might well help to turn the projected electoral map blue once more.

The last year has taught everyone a lot. The politics of unexpected shocks and unprecedented surges should make us all reappraise our basic presumptions. We all need to get used to marginal rather than binary thinking: of subtle shifts in less and more, rather than “x will win and y will lose”. We need to move the dial back and forth, not switch our predictions on and off. And we need to keep an eye out for those small parts of the electoral mystery that we can identify as the moving parts. One thing alone is certain: coming into 2017, we thought we knew where we were going. Leaving it, things look more confused than ever.