Labour’s Green Paper outlining a “post-comprehensive” era in secondary education owes a great deal to a slight, bespectacled intellectual who was until five years ago a Liberal Democrat.

Andrew Adonis, who turns 38 next week, is the Prime Minister’s adviser on education in the Number 10 policy unit. Like his political master, he comes to educational policy-making without the ideological bedrock of traditional Labour - and with little understanding of those who have. And like Blair, he is no great fan of the comprehensive system.

In A Class Act, the book he wrote with fellow-journalist Stephen Pollard in 1997, Mr Adonis said: “The comprehensive revolution has not removed the link between education and class but strengthened it....Comprehensive schools have largely replaced selection by ability with selection by class and house price.”

At Number 10 since 1998, after spells as an Oxford academic and journalist, Mr Adonis has been a forceful advocate for recasting the comprehensive system, and, some would add, expanding selection by the back door.

“Specialist schools - doubling their number within five years - is a very Andrew Adonis thing,” says a friend and fellow-labourer in the political undergrowth. So too are the proposals announced in the past week to open up access to higher education, which could help to break the stranglehold of private schools on Oxbridge and other top universities.

In the running turf-war on policy between the Department for Education and Employment and Downing Street, not everything has gone Mr Adonis’s way.

David Blunkett’s firm veto of top-up fees for elite universities signifies a victory for the Education and Employment Secretary over one of Mr Adonis’s cherished schemes. But in general he is credited with a much higher adoption rate for his radical ideas - others are Excellence in Cities and city academies - than advisers in other areas of policy.

Mr Adonis works his magic by the combination of a formidable brain, a fluent and persuasive pen (“enormously impressive speed of drafting” says electoral analyst David Butler) and a slightly donnish charm.

“He’s a genuinely charming, unassuming, friendly, likeable man,” was one tribute from a former colleague. He is also described as “typical of a certain ind of British intellectual, who totters between taking things deadly seriously and making clear he doesn’t take anything too seriously.”

The son of a Greek Cypriot who settled in north London, Andrew Adonis spoke no Greek at home. He attended a state primary school and then Kingham Hill, a minor public school in Oxfordshire.

After a first in modern history at Keble College, Oxford, he moved effortlessly from the world of academe (a doctorate at Christ Church on the peerage and politics, a fellowship at Nuffield) to that of high-class journalism: (a five-year stint at the Financial Times followed by three years as a columnist on The Observer).While on the Sunday paper, he suggested that Tony Blair should become his own education minister. The move to Downing Street has helped make that almost true.

A change of party was necessary first. A natural liberal with a small “l”, he was a LibDem member of Oxford City Council from 1987-91 and briefly became the party’s candidate for a seat in north Wiltshire. But decided in the mid-1990s that New Labour offered a better chance of realising his policy aims in government.

He lives quietly in Islington with his wife Kathryn, whom he met while tutoring her at Oxford, and their small son and daughter. “Not one of the Islington glitterati,” stresses a friend. “He watches TV, listens to music, reads books.” He became involved in the world of local education politics when he became governor of Islington arts and media school, one of the Government’s “fresh starts”, but resigned when the school ran into fresh difficulties last year.

Although the education specialist at Number 10, Mr Adonis’s wizardry with words means that he spends about a third of his time writing speeches for the Prime Minister (last week’s at Enfield was one of his). Friends say he is “both frustrated and excited” by his role: frustrated by battling with the intractable forces in the education department and by the journalist’s frustration at not being able to comment openly - but excited at the possibilities for action.

Whatever is going on in the bowels of Number 10, it would be surprising if Mr Adonis did not one day use his experiences to write an elegant account of the way government actually works. But first, he might see it from another side. He has not abandoned his parliamentary ambitions and could still find a seat before the next election.