Newington's Mark Glover looks at how turnout and undecided voters will determine the outcome of the General Election.

There is a lot of excitement in the media and among the political classes as we see the polls tighten. Labour creeping up to within three points of the Conservatives (YouGov) has stimulated debate about a hung Parliament which seemed far-fetched at the beginning of the campaign.

Yet, this is very reminiscent of the 2015 General Election when Ed Miliband, a week out, seemed to be making progress with voters and many of the pollsters predicted a hung election. They were proven to be wrong and the Conservatives were re-elected, albeit with a small majority.

The YouGov poll says that 15% of voters are undecided about who they will vote for on Election Day or whether they will vote at all. This could have a tremendous impact on the result. In 2015 they voted Conservative in big numbers.

The other potential impact is differential turnout. Labour reports strong leads amongst younger voters but Conservatives still have a considerable advantage in the over 65 category. The reason other polls suggest the gap is so large is that the older age groups tend to vote more, with turnout amongst the 18-25 year old group being around 40% in 2015. So it matters little if you say you are backing a party unless you are actually motivated to go out and vote for them. Apart from YouGov other pollsters are weighting the support for the political parties against the likelihood of different age segments turning out to vote and within these polls the Conservatives still retain a strong lead above 10%.

With undecideds and turnout being important it is vital for the two main parties to ensure their messages cuts through. So expect the Conservatives to continue attacking Corbyn’s leadership, warning about the dangers of a coalition with the SNP and the risks to the country of Labour’s poor economic leadership. Labour will continue to talk about austerity and public sector investment and will hammer home the message that they are ‘for the many not the few’, saying that Conservatives only look after the rich. Will the result be the same? We don’t know but there are three things that are different from 2015.

Firstly, Corbyn is performing better than expected and is more at ease campaigning than Ed Miliband ever was, so when people meet him in the flesh or see him on television he is probably better than they were expecting. This is diluting some of the effectiveness of Conservative attacks, although he still remains a problem on the doorstep.

Second, the Conservatives have not run a good campaign. The manifesto took them off-message, with the so-called ‘Dementia Tax’ frightening their core vote and Theresa May having to announce a u-turn within hours of the announcement. May’s non-appearance in the televised leaders' debate has also weakened her, with the Prime Minister seeming less at ease campaigning than some of her rivals.

Third, although the Conservatives are running a strong campaign online, Labour has its own new online operation, battle-tested during Corbyn’s leadership campaigns, which has expanded from the overly Twitter focused campaigning of 2015.

Even taking this into account I still struggle to see anything other than a Conservative majority but I am not sure it is going to be as high as the Prime Minister expected.