Rocking back in his chair, hands clasped behind his head, with the tranquil elegance of Westminster’s Smith Square behind him, William Hague is at his most relaxed. He has just been asked whether he can see the day when a Tory prime minister will preside over a Cabinet in which the majority send their children to state schools. “Yes.”

Really? “Yes,” he repeats. And suddenly his trademark smile beams across his face and he says: “Once you’ve got the leader, you’ve got the majority!” His chief spin doctor, Amanda Platell, a former editor of the Sunday Express, bursts out laughing. The Leader of Her Majesty’s Opposition warms to his theme: “The Ayes 1, the Noes 20. The Ayes have it!” If it was meant to amuse, it works. Hague may on occasions have problems with his image - remember that baseball cap - but he can charm as well as any politician.

On closer scrutiny, it’s obvious he is not joking. He is the boss and has made a serious statement of intent. In future, Conservatives with ambitions to rise in Hague’s party will do their damnedest to send their children to the local state school. That, after all, is what Hague, and his wife, Ffion, plan to do with any future offspring.

“I would send them to the local state school. I believe in a diversity in state school provision, but the local schools in my constituency, Richmond (Yorkshire), are comprehensives and I will send my kids to those schools. They’re very good.”

Hague’s party is different from the one led by Harold Macmillan 40 years ago when the majority of the Cabinet was educated at Eton. “The Conservative party has changed. The first party ever to have a leader who went to a comprehensive school is our party,” he says.

Hague takes pride in his “man of the people” comprehensive background. He is equally proud of his Yorkshire roots around Rotherham and Barnsley. Born in 1961, he was the youngest in a close-knit family, with three older sisters. His father, Nigel, ran the family business, Charles Hague and Sons, a small soft drinks firm which also held franchises to deliver alcohol to pubs and clubs in the area. Young William got to know the local landscape on Saturdays from the cab of a lorry.

His mother, Stella, was a housewife, raising four children in a comfortable detached house in Wentworth, a middle-class village in a working-class area steeped in the traditions of the Labour movement. His father used to come home for lunch.

As the only boy, seven years younger than his youngest sister, he was sometimes teased, sometimes spoiled by his siblings. But most of the time he was left to get on with his own interests - toy soldiers were a particular favourite.

Then, aged 11, life changed for Hague when he won a scholarship to Ripon Grammar School, a top performing state boarding school 30 miles away. “It’s a good school. But I didn’t like it there and I left after a few months. I said I was going to run away if I can’t go to another school. A month later it was all forgotten, I was at the local school and never looked back.”

The local school was Wath Comprehensive in Wath upon Dearne. “I always knew I would rather have gone to the local school, where I knew people.”

Once at Wath, he thrived on the varied social mix, making new friends with pupils whose fathers and older brothers worked in the coal mines and steel mills. His friends, many of whom attended his wedding two years ago, included Nigel Parry, now a portrait photographer based in New York, and the son of a miner who is now an orthopaedic surgeon at St James’s hospital in Leeds.

“It was a great school and we all knew that. It didn’t have what you would regard as a classically good catchment area. Sometimes people think that whether a state school is good is wholly dependent on the socio-economic mix of the population around it. My school shows that’s not the case. Actually, if you have good leadership and set high expectations of pupils, you can achieve very good results in all kinds of areas.”

Hague seems to have been a popular boy, an enthusiastic “joiner” who sang in the choir, played a leading role in the debating society and took part in school plays. He was a leader there too, captain of a house.

He worked hard and was successful, gaining four As at A-level and a place at Magdalen College, Oxford. Some accounts of his life as a pupil and student suggest he was a bit of a swot and a loner. He also acquired the reputation of a political “trainspotter”, with an obsession for parliamentary statistics, memorising the size of MPs’ majorities and poring over details about marginal seats.

The impression was fuelled by his joining the Young Conservatives on his 15th birthday. He became an advocate of fashionable causes, mixing support for capital punishment with more liberal views in favour of lowering the legal age of consent for gay sex and support for proportional representation. One choice photograph of the teenage Hague shows him - his toothy politician’s smile already practised - wearing a tweed sports jacket and a National Association for Freedom “I’m a freedom fighter” badge.

But the view of Hague as a political obsessive with no other interests is unfair, says his former politics teacher and mentor, Robert Godber. Now headteacher at Wath comprehensive - and himself a long-time Conservative supporter - Godber paints a very different picture.

“He was very gregarious and had a wide circle of friends who enjoyed their learning at school,” he remembers. “They drank very deeply from the well, both academically and socially. This idea has got around that William shut himself off and read copies of Hansard. He did do that, but all that was borne very lightly.”

Godber recalls that on one school outing to the Lake District the ever energetic Hague got up extra early one morning to run up and down Helvellyn, returning in time for breakfast.

Hague’s seemingly boundless energy (he is still a keen fell walker) is one factor behind his many career achievements. He became, at the age of 16, the youngest speaker to address the Tory party conference. He achieved a first-class degree (in politics, philosophy and economics) while serving as president of the Oxford Union. After business school in Paris and working in management consultancy with McKinsey and Co, he won the safe Yorkshire seat of Richmond in a by-election in 1989 and went on to become the youngest Cabinet minister since Harold Wilson. By 36 he was party leader.

His school background appears to have played a formative part in his development. “It’s certainly given me the confidence of knowing that you can just pull yourself up by your own boot straps,” he says. “And you do feel you know how to look after yourself when you’ve been to a state school in a mixed catchment area. When I got to Oxford I really felt I could cope with everything, often much better than people who’d been to private schools, who to me seemed like they’d had a bit of a sheltered life.”

While not advocating comprehensives for all, Hague says he wants to see an extension of the choice and diversity of policies introduced to the state system by his Conservative predecessors.

“It is not my view that there should be a grammar school in every town,” he says, dismissing newpapers reports to the contrary last month. “But it is our policy to allow different areas to have different structures. In some cases that is grammar schools, in some cases it is not.

“Of course it is our policy to defend the grammar schools that are there, which in almost every case are excellent schools. But we’re interested in excellence in education across the board.”

Hague and his education spokeswoman Theresa May, another product of the comprehensive system, are preparing to launch a major policy initiative at next week’s party conference in Blackpool, setting out new ways of encouraging diversity within the state system. These could include allowing parents to decide whether to introduce academic selection.

He is not, he insists, saying that parents who want a grammar school will always be allowed to have one. But the Tory policy will be to “unleash more choice, competition and freedom into the system”.

There will also be a proposal for “a major extension of the freedom of schools to manage”, cutting back on controls, which could mean giving all schools the independence that existed in the grant-maintained sector.

“Setting schools free will be an important theme: teachers free to teach, schools free to a much greater extent. And that does have implications for their relationships with local education authorities, and we’ll be going into that at the conference too.”

The plans may well silence critics who argue that, since Hague took over as leader two years ago, the party has failed to find an alternative vision to Labour’s top-down approach to raising education standards. “All our policies will be in the direction of more localisation rather than centralisation; less regulation from the centre rather than more regulation; greater diversity of provision rather than less; more choice for parents rather than less; more decision making within a school rather than in Whitehall and the local authority,” he says.

Hague hopes his decentralising message will be popular with teachers. One proposal in particular he hopes will please them: he plans to reverse Labour’s requirement on all schools to cut down on exclusions. He argues that headteachers should retain the freedom to exclude disruptive pupils, as one of the few ways left to them of enforcing discipline. Unruly pupils should be taught in special units - not necessarily within a school - “where there is a regime which encourages them to improve, and has the incentives and expectations for them to improve”.

This is part of a Tory package aimed at tackling disaffection and truancy in secondary schools, which would allow fewer academic pupils to be exempted from the full national curriculum from the age of 14, enabling them to do more vocational education and training.

Following the collapse of the Tory vote among teachers at the last general election, Hague faces a struggle to convince the profession that he sympathises with their problems. Much as he empathises with state schools, his policies look set to inject more parent-led market forces.

But Hague, who calculates that he has visited 80 schools this year to listen to teachers’ concerns, believes he can win teachers’ trust and convince them his party has changed.

“Teachers are not dealing with a Conservative party that is only interested in a few people or doesn’t know about state education. They are dealing with a Conservative party, the leadership of which is steeped in state education, that takes a great deal of time and trouble to know what’s going on, that believes that schools are better when teachers are freer rather than dictated to. We have seen from our own experience that the biggest improvements in results come from what teachers do on site, not what civil servants decide in an office.

“I know there has been a chequered history of relationships between the teaching profession and the Conservative party, and there will still be things about which the teaching profession and all governments disagree. I’m certainly not going to say we agree with teachers about everything. But I don’t think any Opposition for a long time has taken such time and trouble to listen to, be in touch with and educate ourselves about what’s going on in the country’s schools.”

Hague, who hopes to be the first comprehensive schoolboy to become prime minister, will have to wait and see whether the nation’s teachers are ready to put their faith in him.