The battleground for the next election is already becoming clear. The decisive electoral map involves more seats in the North of England and the key voters at the next election will be the aspirational working class and lower middle class voters. Politicians need to do more to appeal to these voters if they are to have any chance of winning an overall majority in 2015.

In the last 50 years, 11 general elections have resulted in a party gaining an overall majority. Three politicians were responsible for nine of these 11 victories and all were successful because of their appeal to the "strivers". Margaret Thatcher, Tony Blair and Harold Wilson were all unique in their ability to appeal to aspirational voters, or those voters clumsily referred to by market research jargon as C1s and C2s. The other two leaders to have won overall majorities - Edward Heath and John Major - also had a unique aspirational appeal.

According to his biographer, the secret of the electoral success of Harold Wilson was that he was: "a reflection of what many people... were seeking: an image... of self-help, energy, efficiency and hostility to upper-class pretension and privilege. It was an image of virtue, endeavour and just reward."

Thatcher, who came from a similar aspirational background to Wilson, appealed to the same set of voters, albeit in different ways to match different times. Her appeal, based on spreading home ownership, share ownership and a belief in meritocracy chimed with the "strivers" of her time.

Blair didn't share the background of Wilson or Thatcher but did share their feel for the aspirational electors. In 2005, he argued that: "New Labour is today the party of aspiration, for middle-class and poorer families; for all. Every time we have ceded that ground in politics, we have lost. Every time we have occupied it, we've won."

Successfully appealing to aspiration is so often the key to delivering election victory in the UK, especially in key marginal seats. It was clear that neither Party at the last election had convinced sufficient numbers of aspirational voters in order to win a majority. According to Ipsos MORI, in her three election victories, Thatcher claimed an average of 40 per cent of the C2 vote (increasing the Tory share by 15 per cent in 1979). Blair averaged 46 per cent of the C2 in his three election victories, increasing the Labour share amongst C2s by 10 per cent between 1992 and 1997.

By contrast, at the last election, the Conservatives could only poll 37% of the C2 vote - only 4 per cent up on 2005. Although Labour's vote amongst the C2s had plummeted from 40 per cent at the previous election to 29% in 2010, not enough of them had turned to the Tories. "Mondeo man" didn't turn out for the Conservatives in 2010 in the same way that he had turned out for Thatcher or Blair.

Both political parties are facing different challenges in appealing to hard-working, aspirational voters. Polls show that the Conservatives are seen by a large number of respondents as "the party of the rich", who don't understand ordinary working people or people from the North of England or Scotland. The same polls, show that Labour are overly identified with trade unions, the poor and public sector workers and don't understand ambition or aspiration.

Crucially, research for Policy Exchange has shown that the country is more aspirational than ever and that appealing to this ingrained belief in meritocracy and aspiration will be a key determinant of the result of the next election. In the research, we asked what people believed that the best conception of "fairness" was. The idea that, "in a fair society, people's incomes should depend on how hard they work and how talented they are" was supported by some 85 per cent of respondents. This was a considerably greater proportion than those who supported either a free market (63 per cent) or egalitarian (41 per cent) conception of fairness.

The findings illustrate the centrality of aspiration to being successful in British politics. The aspirational lower middle class and working class, who are ambitious for themselves and their children, and willing to work hard in order to succeed, remain fundamental to electoral success in the UK. Ed Miliband, with his concept of the "squeezed middle" has begun to understand the importance of aspirational voters.

Appealing to the "strivers" will, of course, require workable policy as well as rhetoric. Issues including developing a quality state education system, reforming welfare and housing policy will be central themes.

Only by tapping in to the aspirational "strivers" will either party be able to win a majority at the next election. So far, neither party has shown itself entirely able to tap in to the aspirational feeling that meant Wilson, Thatcher and Blair could achieve electoral success.

David Skelton is deputy director of Policy Exchange.