Polls can be troublesome, but we can still learn from them and we can win, writes Alex Snowdon

There has been a flurry of discussions about opinion polls in recent days. There are a number of difficulties with polls, but it can be worth looking at the polling to get a sense of where we are in the election campaign - and what trends there may be.

A new poll from BMG slashes the Tory lead from 13% a week ago to just 6%, with the Tories on 39% and Labour on 33%. Three nationwide polls in the last few days have all given Labour 34% of the vote share. They have put the Tories on 41% or 42%. All of these polls had fieldwork conducted after the launch of Labour’s manifesto last Thursday and the following evening’s Question Time for party leaders, from which Jeremy Corbyn emerged very favourably.

Polls can vary significantly, but here we have a distinct pattern. Polling since the manifesto launch has shown Labour increasing its vote share and making progress in closing the gap. The Tory vote is holding up in the low forties and has been helped in recent polls by the Brexit Party standing down from hundreds of seats.

A much-trumpeted poll by YouGov predicting a sizeable Tory majority should, despite a very large sample, be treated with great caution. The research was conducted before the Labour manifesto launch and it therefore cannot register any impact of that.

At the start of the election campaign, the polling average was 35% for the Tories and 25% for Labour. It was always likely that both parties would increase their support as the election campaign progressed. This, in fact, is the big trend of the campaign: a growing polarisation where the two viable parties of government increase their support at the expense of minor parties.

This was fairly predictable for a number of reasons. The combined vote share for the two main parties in 2017 was well over 80%. An actual election concentrates minds on the big question of which party will form the next government. It was always likely, given what happened in 2017, that Labour support would grow once a campaign got underway and the party could promote its message and policies widely.

Two other things have boosted this polarisation. The Lib Dems have struggled - to pit it mildly - with Jo Swinson’s Question Time leaders’ debate performance symbolising the party’s problems: narrowly preoccupied with Brexit, tarnished by five years in coalition with the Tories, devoid of appealing policies. The other factor is the Brexit Party standing down in Tory-held seats, which could make it a little tougher for Labour to crack many of its target seats.

The polling trend is both the same as in 2017 and different to 2017. It is the same because Labour vote share has grown considerably. It is different because Tory support has grown too.

The first fact should be very encouraging for Labour supporters. Like last time, the effect of campaigning - of announcing popular new policies, getting Labour front benchers into the media, leafleting and canvassing, and so on - has been very positive. Crucially, the political debate has widened from the miserable and narrow obsession with Brexit.

The second fact - the Tory rise in the polls - should be a cautionary warning, but not a reason for despair. It would be naive to assume that Tory support will fall. That simply isn’t the trend so far at all. The crucial challenge for Labour is to keep increasing its support, especially in marginal constituencies.

A lot can still change in the remaining days of the campaign. One of the great unknowns is turnout: not merely the headline figures, but the demographic breakdown. The polls are all weighted to account for the likelihood of people voting, in particular according to age. Younger respondents are assumed to be less likely to vote, while older respondents are regarded as more likely.

This weighting may turn out to be correct. However, the surge in voter registration, especially among the under-35s, shortly before this week’s deadline could indicate something better for Labour. Getting the vote out will be crucial.

The Tory strategy all along has been voter suppression: retain its own voter base and hope that Labour cannot catch up. Hence not a single appeal from the Tories for people to register to vote, the deliberately safe and low-key approach to the campaign (like avoiding TV debates where possible and an exceptionally cautious manifesto) and a focus on negative spinning about Labour, especially about Jeremy Corbyn.

Labour’s approach is the opposite: do everything possible to enthuse, inspire and galvanise potential voters. Keep up a constant flow of policy announcements, make a big splash with the manifesto, take the TV debates seriously and use them to generate shareable social media content.

Labour’s big weakness may turn out to be the concessions it has made - progressively over the last two years - to those pushing for a Full Remain stance. This appears to be costing it support in many marginal seats which had a comfortable Leave majority in the 2016 referendum. A relentless focus on class issues that bridge the EU divide - NHS, schools, housing, climate change and more - is required between now and 12 December. It may or may not be enough to overcome the damage already done.

This is a reminder, too, that the general election outcome depends ultimately on what happens in particular constituencies, not the national vote share. The Tories’ great advantage has been money, with high levels of donations from wealthy backers, channeled towards target seats. The great asset for Labour has been, and continues to be, its formidable army of campaigners, including many who are new to election campaigning.

The impact of that campaigning is currently one of the things that is hard to predict. The latest polls make it clear that Labour support can grow and a Tory majority can be prevented. At the same time, an assumption of a repeat of 2017 would be naive. It is all to play for.