The pollster changes, but the result remains the same: Labour miles off the pace in the polls. But that the polls got it wrong in the 2015 election means some Labour supporters are holding out hope for a repeat. Are they right to do so?

As far as the general problems of polling are concerned: the Brexit referendum was a failure of punditry not of polling. The polls showed a dead heat but they were written up as pointing strongly towards a Remain vote. In the United States, the polls actually got the nationwide picture right but Donald Trump managed to win because his vote was well-distributed to benefit under the rules of the American electoral system.

They have had big problems picking up the scale of the victories in the French primaries, in which both Benoît Hamon and François Fillon overperformed their final polls. That may mean that the French polls are off a bit. Equally, both those candidates were enjoying a surge in support, which the polls did detect. If Jean-Luc Mélenchon continues to soar in the polls, getting 22 per cent, 23 per cent and then gets 25 per cent on the day itself, are the polls wrong? Not really.

That doesn’t mean, however, that the polls in Britain can’t be wrong. But when they are, they tend not to match the more important information: that is, the elections going on in the country as a whole. Throughout the last parliament, Ed Miliband did significantly worse at local elections and parliamentary by-elections than his poll rating suggested – he went on to lose. Under Jeremy Corbyn, up until the referendum, he did about as well as you’d expect according to the polls – that is, a little bit worse than Ed Miliband.

Then a combination of forces hit Labour’s vote share: the failed attempt to remove Jeremy Corbyn knocked Labour from 29-31 per cent to 25-27 per cent. The popularity of the new Conservative leader, Theresa May, increased their vote share into the high 40s, a force that was aided by the post-referendum collapse of Ukip.

Both Theresa May’s popularity and the effects of the coup have diminished somewhat, but the collapse of Ukip continues to benefit the Tories, while the Liberal Democrats have enjoyed a post-referendum revival.

The parliamentary by-elections and council elections all suggest that the picture we’re seeing in the polls are broadly accurate, with one minor caveat: the Liberal Democrats are doing better than we’d expect, at the expense of both parties. However, the Conservatives have gained former Ukip votes to make up for what they’ve lost to the Liberal Democrats – Labour has not regained the bulk of its “Labour 2005, Ukip 2015” vote but is losing its “Liberal Democrat 2010, Labour 2015” vote.

My instinct is what is happening is what usually happens to the Liberal Democrats in opposition – people forget about them until election time, when they decide that they aren’t such a bad option after all. (Or, at least, when they decide that they are better than the other options available.)

My strong feeling is that this will hold at the next election and while it will hurt both parties, the effect will be more noticeable on Labour’s vote share. But one very important thing to watch out for in terms of the next election is how the Liberal Democrats do across the country on 4 May.

There are a couple of other things to watch out for. As with Ed Miliband, Jeremy Corbyn’s leadership ratings are below that of his party’s. My expectation is that during a general election campaign, those two numbers will start to converge – some Labour voters will warm to him as he is the Labour leader, while some Labour voters will go off Labour as the party is led by Corbyn. If Labour goes into the short campaign in 2020 on 22 per cent and with its leader on 13 per cent, I expect they’ll end up polling 19 per cent.

There is one major caveat, however: the debates. The success of Jean-Luc Mélenchon is reminding us of something that Nick Clegg demonstrated in 2010: a good debate performance can get you a hell of a lot. Mélenchon has fewer ideas than Benoît Hamon, the Socialist party candidate and his rival on the left, but gave a much better performance than him, allowing him to cohere much of the left vote under his banner.

How Corbyn performs in the 2020 debates could transform Labour’s prospects. That he regularly gets the best of May at Prime Minister’s Questions, means that his debate chances aren’t bad. But a poor performance from him – or a strong one from Caroline Lucas or Tim Farron – could spell further disaster.