In June 1995 I told some of my university contemporaries that I was planning to vote Conservative in the next general election. The reaction among a range of 20 to 22-year-olds at Cambridge ranged from shock (“how could you?”) through disgust (“after they’ve ruined the country too”) to stunned amusement (“well you always were a bit odd”). Ten years later most of them think the same thing.

This is the issue that the legions of commentators and post-election experts have passed by in the polls: the generation born between the mid-1960s and the mid-1970s do not vote Conservative. They did not in this year’s general election. And they give every sign that they will not in the next.

This is the generation that grew up with car phones and Madonna, with Loadsamoney and the miner’s strike. Their early political memories are of Spitting Image and Norman Tebbit. They came of age under the poll tax or during the early-epoch, whiter-than-white phase of Tony Blair.

This generation, in short, were brought up to think that chinos were what you were meant to wear and that voting for Margaret Thatcher was certainly not what you were meant to do. They are “Generation Gap” — those who know how to dress conservatively, but just do not vote Conservative.

Generation Gap as a whole are more Thatcherite and entrepreneurial than their parents. They are more confident and better travelled. They are more socially liberal but still keen on moral standards. The key reason they don’t vote Conservative is that they don’t think Tories care, and they don’t like Tory values.

In the May general election, only 25% of Generation Gap voted Conservative — 8% less than the national average. If half that 8% had voted Conservative, Tony Blair would have lost 12 more seats and been left with a majority of 44. If Generation Gap had voted in line with the national average, Blair’s majority would have been reduced to an unstable 20-24 — just like John Major’s in 1992.

In the past three elections Generation Gap have been consistently the least likely to vote Conservative. And even though they are now reaching middle age they are still not. In previous generations young voters started voting Conservative as the weight of mortgages, education and tax began to press — in short, as reality bit. This one has not. Staggeringly, young voters of 18-24 were more likely to vote Conservative in the general election than those in their late thirties or early forties.

We are facing a lost generation of Conservative voters. It is an important generation, too. Everyone knows about the baby boomers — the rush of post-war births from 1946 to 1948. Well, those baby boomers grew up and had children. And they had them between the mid-1960s and the mid-1970s. From 1965 to 1970 the birth rate was almost 20% higher than 10 years later. Today there are 2m more British people in their thirties than in their twenties.

In an age of low turnouts, Generation Gap are big battalions. They are beginning to play a pivotal role in national life. As their new companies grow or as they take over old institutions they invest them — and public life — with a less formal culture and a new set of priorities.

Think about the significant public figures in or just out of their thirties: Charles Dunstone, multimillionaire founder of Carphone Warehouse who works in Acton and takes the Tube to work; Andy Hornby, chief operating officer of HBOS at 38, who has helped bring a new American style of retailing; the directors of at least five influential think tanks; the secretary of state for education; half a dozen bestselling authors; a clutch of the most respected journalists. To say nothing of the scores of thirtysomething bankers and investors running half the deals in the city. Britain is changing, and Generation Gap are in the engine room.

Winning Generation Gap is crucial for any political party. Their support is a necessary precondition of power. But what do they believe, and why don’t they vote Tory? A glance at the evidence is both surprising and familiar. In some ways, Generation Gap are the generation that has gained most out of the Thatcher economic transformation. They are more entrepreneurial, richer and better travelled than their parents, having learnt to work in the long boom of the 1990s.

Generation Gap are more free-market than their parents. Perversely, given how they vote, they are Thatcherite. They work hard and are optimistic.

They are sceptical of the unemployed’s inability to find a job (76% believe they could find a job if they wished — more than any other age group). They believe in enterprise and low tax (a minority under 35 believe the government should tax and spend more). They don’t support environmental legislation any more than their parents or grandparents do.

They are also less communal and local than their parents. They are less likely to look out for their neighbours and shyer about asking for favours from them (only 29% would feel comfortable borrowing a fiver; 38% of their parents would). They spend less time helping charities. They spend less time with their friends. They know fewer of their neighbours. They are less defined by place, more by career or “lifestyle”.

Although Generation Gap are more socially liberal and less tolerant of authority than their parents, they are not dramatically more liberal: 77% think the young need more discipline — only marginally fewer than their parents. And more in their twenties and thirties blame immigrants for crime than do those in their fifties. A majority of Generation Gap even support censorship “to uphold moral standards”.

However, Generation Gap have been conditioned not to vote Conservative. Only 31% of those aged 25-34 think the Conservative party shares their values — 5% less than those aged under 25 and 10% less than those aged over 55.

This is the next challenge in politics. As the Blair era ends and as Labour’s freehold on power looks finite, the party that can capture Generation Gap will win power. They are the key that unlocks at least two dozen crucial parliamentary seats. There is no reason why Conservatives cannot win their hearts, minds and votes.

The Conservatives can speak to Generation Gap’s concerns not by abandoning support for the free market (which Generation Gap share), nor by retreating from the need for radical public sector or welfare state reform (which is also accepted), but by clearly, consistently and passionately making the case for a fairer Britain.

Unless the Tory party can convince Generation Gap that they are like them, hard-working, fair people, interested in others and not out to get the weak, it can pack up and go home.

Nicholas Boys Smith is a professional strategist and former Conservative front bench adviser. This is an excerpt from True Blue: How Fair Conservatism Can Win the Next Election, published later this month by Demos