Ashcroft joins Populus in putting Labour up 5 points: What's changed?

Labour have ticked up, but the more obvious shift in Ashcroft's poll has been a 2-point Tory-to-Ukip swing.

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This post originally appeared on May2015.com, our elections website.

Two polls are out today and they have handed an unexpected boost to Ed Miliband.

First, Populus, who poll twice a week, handed Labour a 5-point lead this morning. For the past month they have polled Labour slightly higher than everyone else – the average of 45 polls since 23 October has given Labour a 1-point lead; Populus' nine polls in that time have given them a 1.7-point lead – and on Friday they put the party ahead by 3, so the poll was less impactful than it may have been coming from, say, YouGov, who are now consistently showing a tie or small Tory lead.

But Lord Ashcroft has now joined them in putting Labour up by 5. Here's how those polls compare to the 47 others we have had in the past month.

The vote shares in each poll are quite different. Populus put the Tories on 31 per cent, Labour on 36 per cent, the Lib Dems on 9 and Ukip on 15.  Ashcroft has the major parties significantly lower – he put the Tories on 27, Labour on 32, the Lib Dems on 7 and Ukip on 18.

But what has changed each pollsters' numbers? What types of voters have changed their minds in the past few days (Populus) or week (Ashcroft)?

At first glance, there is little cause for the Tories' fall in Ashcroft's numbers. They are two per cent lower this week than they were last Monday, but their 2010 vote share is unchanged from last week, at 70 per cent. That's the number of 2010 voters who are planning for the party again, excluding those who don't know.

The significant change is the Tories' fall in support among those who didn't vote for a major party in 2010.

Support for the Tories among 2010 Lib Dems is slightly lower this week, but not by enough to account for a 2 per cent fall. The cause is hidden: the week-on-week change has been in the number of Tory supporters among those who supported none of the three major parties in 2010, which isn't shown in Ashcroft's "cross-breaks" or "sub-polls". These break down the poll's respondents into demographics, such as age, gender, and how they voted in 2010.

The significant change is that this week the Tories only attracted 14 per cent of those who didn't vote for a major party in 2010 – last week they won over 24 per cent of them. Most of that support has gone to Ukip. Last week 34 per cent of these voters backed Farage's party. After winning their second MP in Rochester, 48 per cent of them now back the party.

This explains the 2 per cent swing from the Tories to Ukip in this week's poll. It should also possibly reassure the Tories: this swing may just be the result of yet another round of publicity for Ukip. The polls may change next week. We've seen this in Ashcroft's polls before. After the furore over the leaders' debates the Greens reached 8 per cent in his polls. A week later they had fallen back to 5 per cent.

Labour haven't suddenly won back their core 2010 vote.

As for Labour, they have ticked up from 30.1 per cent to 31.8 per cent in Ashcroft's polls. Their is no single reason for this - their support is just very slightly higher among all 2010 voters. They haven't suddenly won back their core 2010 vote. Last week they won support from 76 per cent of them – this week they won 77 per cent.

Those, like Tom Watson – who quickly declared that Lucy Powell and her "focus and message" have transformed the party – should wait for a few more polls before declaring any newfound success.

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Harry Lambert was the editor of May2015, the New Statesman's election website.