Anthony Horowitz is on his soapbox. He's adamant he doesn't want to be there – he's been forced to step on to it in outrage at the way children are treated these days. Now he is there, though, he might as well get a few things off his chest.
"The last thing you want is a children's author on a soapbox," he says. "It's an unpleasant sight, and it's misguided to think that, because you have influence over what children like to read, you have any authority to speak on their behalf."
Just try stopping him, though. "What we've done over the past 13 years is utterly to demonise kids; to alienate them; to separate them from ourselves – as if they're not actually what we once were. The Government has done everything in its power to marginalise them, turn them into little bleeps on a database, surround them with even more foolish laws, even more foolish targets, to manage every aspect of their lives from cradle to the grave. And the bitter fruits of that misjudgement and selfishness are becoming ever more apparent."
He is warming to his theme, citing the recent attempt to vet children's authors before they visit schools, something he has campaigned against vociferously. "I was at a school the day before yesterday," he says. "They told me that they had just spent £4,000 on vetting: £4,000 to undermine their own trust in each other, £4,000 that could have been spent on books, sports equipment, on painting a classroom, getting a new computer."
To be fair, he speaks a lot about his work as one our most prolific writers, pausing regularly – with no hint of false modesty – to ask: "Am I talking crap?" and "Is this what you really want to hear?"
He confesses that he has been boring his wife. But, again and again, he returns to what he considers the political failings of the Labour Party. In truth, he has little time for any of the mainstream parties. He will be voting Tory at the election, but with little enthusiasm.
His touchstone themes are "values" and the "soul" of the country. "The polls show: do we think that David Cameron and the Tories are going to be any better? No. But what I do think is that we have to stop the erosion of values: it's not to do with the economy, funnily enough; it's more a fight for the soul of the country."
Whew! But what about the day job? Horowitz is, of course, famous for the phenomenally successful Alex Rider books, which centre on a 14-year-old boy who becomes a spy. He is celebrating the 10th anniversary of the publication of Stormbreaker, the first in the series of eight. They are being re-released, which is why we are talking. Another two are planned. To date, the saga has sold around 12 million copies and made their author – already a stranger to poverty – extremely rich.
He has also penned some of the best-known television series of the past three decades, from Robin of Sherwood in the 1980s, to Poirot, Midsomer Murders, Foyle's War and last year's acclaimed Collision, about strangers whose lives intersect around a car crash.
Naturally enough, he is looking around and wondering what life is all about. "I've earned enough money," he says. "I've made my name. I've achieved 80 per cent of the ambitions I had when I was 13. So, I can get fatter and fatter and richer and older, or I can help a little bit in the ways that are available to me."
His political gestation has been slowly gathering speed until, he says: "It just suddenly happens, a strange metamorphosis which is not particularly welcome. But eventually you start thinking to yourself: 'Someone has to speak up for kids, and if nobody else is doing it a children's author might as well.'"
Now he's at a stage when he feels confident about voicing his ire at New Labour: "Honesty and politics parted company about the same time as Alastair Campbell became director of communications to Tony Blair."
He adds: "As a sentient person I've got to have some kind of response to what's happening and I've channelled it into my books; the anger of the Alex Rider books about a kid who's being lied to and manipulated. The books have a strong political edge to them. If there's any secret to their success it's the timing of them – the Iraq war and disillusionment with New Labour. Alex is so betrayed, he's unrewarded. He does good things but nobody seems to notice or care."
In case anyone should level the accusation that he is an armchair critic, he points out that he isn't just a talker but a doer, spending a lot of time visiting schools. Oh no! He's off again.
"There are so many kids who are lost. The ones who don't get jobs, who come out of university and find there is nothing for them: kids who are finding there is no possibility of housing; kids who are coming out of university with vast debts around their necks. That's on top of the debt from the bailout of the banks. What a start in life!"
His oration is entertaining: he is articulate and well-spoken, plummy even. He looks a good deal younger than his 53 years, not just because of his casual jeans and suit jacket. His hair is still dark and he is trim.
In keeping with his youthful demeanour, he lives in a fashionable part of east London. Home is a three-storey converted warehouse in Clerkenwell. Entry is via a small lift, hidden behind a pillar, which deposits you directly into his hallway. He's standing there ready to greet you, an elderly brown Labrador thumping its tail against the polished wooden floors. It feels ever so slightly James Bond.
Born into a wealthy family, Horowitz wrote last year about his unhappiness as a child at boarding school, where he was regularly whipped by the headmaster. He wanted to be a writer since he was eight, and had his first book published at 22 ("I met an agent at a party"). By the time he was 30 he was writing for Robin of Sherwood, which starred Jason Connery, son of Sir Sean, and Michael Praed.
"That was like stepping straight on to the highest rung of the ladder. No climb up to the top for me in terms of television writing." No years of rejection slips and poverty, either, the normal lot of the writer.
But he rejects the idea that it's all been plain sailing, pointing out that for the best part of 20 years he was a jobbing writer before Alex Rider took off. In fact, he nearly packed in children's writing to concentrate on television before the opening line of Stormbreaker – "When the doorbell rings at three in the morning, it's never good news" – popped into his head.
And he has had his disappointments. "I'd like to have directed in the theatre, which is what I set out to do," he says. "I tried to get into the Bristol Old Vic and they wouldn't have me. I was too quick to get a job at 18; too safe.
"If I have any regrets it's that I didn't sow any wild oats between the ages of 18 and 25: really, I should have gone off and got into trouble. The plays I've written have been panned. But you have to embrace failure. I'd also like to write a big film that succeeds."
And then there is his mother. Earlier this year Horowitz revealed that he had considered a mercy killing in the last weeks of her life, as she lay dying of cancer. "Because of what happened with my mother, I've always been resolutely in favour of euthanasia. But as with so many things in modern life, politicians refuse to connect with the argument," he says.
"There was no question she was dying. She was like a Nazca mummy at the end of it, hunched up, her knees drawn into her stomach, her face drawn, and that will always be my last memory of her. It's a non-argument to say somebody will be forced to die against their wishes, because it's an argument against anything on this planet. Drinking milk – somebody might get drowned in it; buying a car – somebody might get run over by it. And now one has Dignitas opening up its luxury hotel in Switzerland, which I will certainly book into."
He's back on the soapbox again, adamant that, like his best-known character, he is being dragged, reluctantly into politics: "Alex Rider was created by me, so obviously there are connections between us. He fights bad guys with gadgets and fisticuffs and chases, and I suppose I'm fighting with my books and my opinions."
A life in writing
1956 Born in Stanmore, Middlesex. His businessman father was a fixer for Harold Wilson.
1964 Sent to Orley Farm boarding school in Harrow, where he says the headmaster "flogged the boys until they bled" and he had a "brutal" time.
1977 Graduates from York University.
1978 His first book, The Sinister Secret of Frederick K Bower, is published.
1986 Writes for the ITV show Robin of Sherwood.
1988 Marries Jill Green, a TV producer, in Hong Kong. They have two sons.
1997 Begins writing for ITV's Midsomer Murders.
2000 First Alex Rider book, Stormbreaker, appears.
2002 Creates Foyle's War, a Second World War detective drama, for ITV. The Gathering, a horror film for which he wrote the screenplay and which stars Christina Ricci, is released.
2006 The film of Stormbreaker is released but critics say it lacks the excitement of the book.
2009 Collision, a five part drama about the lives of those involved in a car crash, airs on ITV.