The current predictions for the 2015 election place Conservatives and Labour neck and neck with projections of around 280 seats each. The most likely outcome of the general election would seem to be another hung parliament. But the vagaries of the British election system mean that small changes in voter behaviour can make big differences in outcomes.

Labour would gain an overall majority with a 5% swing, and the Conservatives need only 2% swing from the 2010 results for outright victory. The fact is that the outcome of the election is likely to be decided by a small group of people in less than 100 constituencies. Indeed, in most elections 90% of seats have remained with the incumbent party.

Appealing to the median voter

The consequence is that parties are after what Anthony Downs called the median voter: the point where the majority of voters' views aggregate. The traditional view is that the median voter is at the centre of the ideological spectrum.

Labour can assume it has the votes left of centre, and the Conservatives assume they have votes to the right – these are the so-called core voters of the parties. So, electoral strategy for Labour is to win over those voters just right of centre (the focus of the Blair approach) and for the Conservatives to grab enough of those just on the left.

This view of voting behaviour is deeply entrenched in both parties after long periods in the electoral wilderness. For Labour, the accepted wisdom is that leftist policies alienated voters in the 1980s. For the Conservatives, the perception of them as the “nasty party” kept them out of office from 1997-2010. Consequently, the electoral strategy of both parties is to avoid a bold narrative that may scare the centre.

Converging on the middle ground

So far, Labour’s economic policy accepts the assumptions of austerity economics and commits a future government to reducing the deficit, in order to emphasise their economic responsibility. It also plans to crack down on “welfare scroungers” and the “job shy” by maintaining conditionality on the job seekers' allowance.

Labour’s tactic on immigration seems to be to avoid the issue (seeing it as one they cannot win on) but talk tough when necessary with more border controls and fingerprinting of illegal immigrants.

Similarly, the Conservatives have emphasised their commitment to reducing the size of the state and cutting welfare spending, through measures like the benefits cap. Yet, they continue their commitment to the most costly elements of the welfare state: health, pensions and education.

The Conservatives realise that they cannot cut the welfare services that their voters use. Any assault on the core of the welfare state may lose them the election.

The end result is that Labour and Conservatives sound similar on welfare, immigration and the economy. This cautious, median vote strategy may be a low risk in a normal election. But this is not a normal election. Recent polls illustrate that this is not a two horse race between Labour and Conservative.

Shifting voters

Everyone has a UKIP problem.Gareth Fuller/PA Wire

Rather than gathering at median position at the centre, voters are now shifting to new points on the left-right spectrum. Neither party can assume its core vote. Labour’s disillusioned voters are shifting to the Greens (now reaching 9% in recent polls), and even UKIP, with Peter Kellner estimating that 23% of UKIP votes come from Labour.

Most worrying for Labour is that in Scotland the SNP seems to be seriously damaging Labour seats. The latest Ashcroft poll suggests that Labour will lose 35 of its 41 Scottish seats, and that this will prevent a Labour majority.

Of course, the Conservatives face a similar problem with UKIP. The latest polls place UKIP on 14%, presenting a real challenge to an overall Conservative victory.

A ray of hope

The problem for both parties is that while UKIP and the Greens may not win many seats, they main gain enough votes to prevent the major parties winning marginal seats, and so create a new level of unpredictability in the final outcome.

The Conservatives, at least, have one ray of hope. As the recent UKIP defector Amjad Bashir reminded us, UKIP exists to get an in/out referendum on Europe. The Conservatives are now committed to such a vote, and paradoxically the only way UKIP will get the European referendum is if the Conservatives win. They do not have an incentive to damage the Conservatives now they have pushed David Cameron this far.

Misdirected efforts

While Labour and Conservatives have a median vote strategy, they are not, in fact, appealing to the voters they need to win over in order to form a government. The fundamental problem is that they do not have the strategy to tackle a more general loss of faith in the traditional political classes.

This is a time when people are attracted by the distinct narratives of UKIP, the Greens and the SNP. Instead, Labour, the Conservatives and the Liberal Democrats are fighting mildly over an amorphous middle ground.

Martin Smith has received funding from the ESRC