This isn’t another discussion about whether Labour can ‘win’: I’m far less qualified than others to make predictions of that kind. Nor is it the appropriate point to ask whether the Parliamentary Labour Party (and to a lesser extent myself) were wrong to think a Corbyn leadership would be disastrous: that discussion should be postponed for a week. Instead I want to ask what the Labour surge tells us about the way political information has been disseminated in the UK.
Sir David Butler says “the movement in the polls over this campaign is bigger than in any election I’ve covered since 1945”. (Some data here.) There are three obvious explanations for this surge. A terrible Conservative campaign which led many to think Theresa May had serious failings, a good Labour campaign which led many to think Jeremy Corbyn was not the ogre some said he was, and a Labour manifesto which contained popular policies. The point I want to make is that none of those developments should have come as a surprise. Yet to the parts of the electorate that created the surge they have been a surprise enough to change their vote.
I have talked about Theresa May in an earlier post, and none of the failings that the campaign has exposed were out of character. For example the ‘dementia tax’ U-turn was little different to the U-turn on self-employed tax. One thing that was clear about Jeremy Corbyn is that he runs good campaigns, and the idea that his appeal would be precisely limited to Labour party members was never likely to be true. (Whether it can extend to older Conservative voters we have yet to see.) Finally it was clear to me from the start of his leadership that he would try and adopt policies that were popular, robust and which most MPs could live with. Those that suggest the manifesto marks the end of UK capitalism have no credibility, as an examination of other European countries would demonstrate.
So if May’s weaknesses and Corbyn’s strengths were pretty clear before the campaign began, why have they come as a surprise to those involved in answering the questions of pollsters? The difference between an election campaign and everyday politics is that in a campaign politicians get more time to talk directly to the people. Outside of a campaign, politicians have to rely more on the media to get themselves and their policies across. So part of the story behind the surge is a failure of the media to accurately portray the abilities of politicians. 
I’m not talking on this occasion about the bias of the Tory press, because if this was all we would see swings to Labour during every election campaign, and that normally does not happen. More important I think is a failure of centrist and left leaning commentators, who almost all took one side in Labour’s internal divisions. The impression many gave was that Corbyn was hopeless and his policies would be laughed out of court. When neither turned out to be true, his and his party’s popularity improved dramatically
Unfortunately for Labour supporters there is a potential corollary. One idea I have seen put forward is that the polls may be exaggerating the surge because those being polled are paying more attention to the campaign than the average voter. All of the factors I identified above may be having proportionately more impact on voters being polled. (This might explain why many Labour MPs say they do not recognise this surge.) All the more reason to leave retrospectives on Corbyn's leadership until after the vote.
 Another factor is Brexit. May emerged as Conservative party leader in chaotic circumstances, without even having to win a contest among Conservative party members. In such chaos, she did not get the scrutiny she deserved. Politics since then has been mainly about Brexit, and while the Conservatives largely united behind May, Labour were more divided. The election was a reminder that other really important issues exist.