One of the more interesting trends since the election was called is the increase in the Labour vote. Although the Conservatives are still miles ahead, thanks to their almost complete absorption of the Ukip vote, Labour is creeping back up to its 2015 level – that is, close to 30 per cent of the vote.

Before the election was announced, I thought one of two things would happen in May 2020: either Labour would find a way to increase the number of people who think that Jeremy Corbyn should be Britain’s next Prime Minister (as low as 14 per cent or as high as 21 per cent depending on the pollster), in which case they would have a chance of winning. Or the numbers of people saying Corbyn was the best Prime Minister and the numbers of people saying they would vote Labour would meet in the middle – some Labour voters would warm to Corbyn as he is the Labour leader, others would go off Labour as the party is led by Corbyn.

Instead, neither of those things appears to be happening. The number of people saying they want Corbyn to be Prime Minister is unchanged since the election. But Labour’s vote share isn’t falling, it’s rising. Why? Here are some theories.

Labour are fighting a very good campaign

As I’ve said before and will say again, the only bits of an election that matter are the bits that people who don’t care about politics see: the newsbreaks between songs on music radio, the pictures that play without sound on Sky News in every Wetherspoons through the country, the few minutes at the start of the six and ten o’clock news before people switch channels – or the few minutes at the end before they switch back.

Labour has a great message for those places – a series of popular policies, largely drawn from the social democratic mainstream though with the odd radical flourish such as abolishing tuition fees. There’s a golden thread as there was to the party’s campaigning in the Easter recess: Labour will do something for everyone by getting the wealthiest to pay more, whether that be ending the VAT exemption for private schools, increasing taxation on private healthcare, or undoing the Conservative cuts to corporation tax.

There’s a criticism to be made that these policies are only fixing one of Labour’s Miliband era problems – people weren’t sure what they were for – but doubling down on another, that people worried that Labour would “spend too much”. Certainly, that many more people are saying they will back the Conservatives shows the limits of that approach. But its benefits may be seen by its increase in its vote share.

People feared Ed Miliband, they don’t fear Jeremy Corbyn

One of the things that was very clear to me in the run-up to the last general election when I visited marginal seats is that people who had voted Labour in 2005 but Conservative in 2010 were actively frightened of an Ed Miliband-led government. They were particularly unhappy about an Ed Miliband government that would in fact be “run” by the SNP, but that wasn’t their only fear. The mansion tax – which hits only a handful of homes in London and would have touched not one house in any of those constituencies – was mentioned, as was the idea that Miliband was a weak leader who had “knifed his brother in the back”. (I’m not wholly sure how these two ideas were reconciled with one another, but there you go.)

But because of the polls, those same people genuinely thought that Miliband would be in government.

Now, the number of people who think Jeremy Corbyn will be Prime Minister after 8 June is smaller than the number of people who think the Moon landings were faked. People are simply not very worried about Jeremy Corbyn. That may mean that voters who flit between the two are instead voting for their local representatives or to lessen the Tory landslide.

The Liberal Democrats are doing poorly

If you don’t like Jeremy Corbyn and don’t trust Theresa May, who do you vote for? The usual answer in British politics is the None-of-the-Above party or the Liberal Democrats as they are officially known.

Although Tim Farron has ambitions to establish his party as a genuine alternative to the Tories, not just a repository for disaffection, the assumption of many – including me – was that whatever happened, the party would get the votes of Conservative voters who didn’t like May and Labour voters who didn’t like Corbyn by default.

Although the Liberal Democrats did outperform their national vote share a bit in the local elections, they didn’t do so in very many places they could realistically win on 8 June.

If you look at their campaign, you can see why. Tim Farron has been on the defensive over his views on homosexuality. That Labour are doing better also means the hunger for an alternative in that quarter is not what they might have hoped. And the majority of diehard anti-Brexiteers are concentrated in the big cities, where they cannot hope to overcome Labour’s large majorities.

The polls are wrong

In 2015, there were two mysteries about the polls. The first was the large number of Labour voters saying that they would vote Labour but they didn’t want Ed Miliband in Downing Street or Ed Balls at the Treasury. The second was how to reconcile the polls with Labour’s weak performance in local elections in 2011, 2012, 2013, and 2014. As I tweeted on the night of the European elections, they were the performance of an opposition heading for the knacker’s yard, not Downing Street.

Then at the general election, the mystery was solved: Labour voters saying they didn’t want the Eds near power weren’t Labour voters at all. Instead, they voted for the Conservatives.

Two years later, the same mysteries are present. If Labour’s vote is increasing, why was it down three points in the local elections last week? Why did the Conservatives do better than the polls would suggest, registering the best performance by a governing party in the local elections since 1974? And why do 30 per cent of people say they’ll vote Labour when at the outside just 21 per cent say they believe Jeremy Corbyn is the best Prime Minister?

Read more: Is Labour really as doomed as it seems?

The systematic error of British pollsters is to overstate the number of people who are going to vote for the Labour party. All of the pollsters have implemented measures to fix that problem after the 2015 debacle. But they did the same after the 1992 election, and that clearly didn’t work. (It didn’t even work all that well in 1997, but Labour did so well that no-one really noticed that the opinion polls had slightly overstated Labour’s strength in the country.)

It may be that once again, the pollsters are simply overstating Labour’s popularity.