Portly, dishevelled, distracted and apologising for being late out of the Almeida Theatre's rehearsal room where he is directing his latest play, Stephen Poliakoff is clutching a sandwich that has every chance of surviving lunchtime. In fact, so constantly qualified, re-phrased and perennially adjusted are the unbroken sentences spoken by the writer and director, the sandwich may make it through the day.

It may be 12 years since he wrote for the theatre, but as Poliakoff says, "It's not as if I haven't been doing anything else in that time." No it's not. He has been busy being the finest television dramatist of his generation. Or at least, the finest in this country. But it all started with theatre. "I never meant to be away from the theatre for as along as that, its just because the television work became all-consuming, to direct, edit and so on. I mean since 1999 I've made the equivalent of about 12 two-hour feature films, that's a lot, and it takes me a long time to write a play, between eight months and a year and so I really had to clear the decks, and I was about to clear the decks when Glorious 39 came along and then I thought I've just got to write a play otherwise I'll never…"

We will probably never know how that sentence ends. But it is not unreasonable to assume that Poliakoff, who these days directs all his own work, is about to say that if he didn't write his new play My City when he did, he may never have written another play. But already he is off on another track, delving into the urban world in which My City is set.

We can catch up a little later. But for those who are unfamiliar with the Poliakoff oeuvre, the last dozen years have seen him direct some of Britain's finest acting talent in some the best television dramas, all written by him. The stars include Michael Gambon, Bill Nighy and Miranda Richardson in award winning BBC plays, and David Tennant and Ramola Garai in Glorious 39, Poliakoff's film of two years ago which revealed how some of Britain's establishment worked to appease Hitler.

The new play is rare, and not just because Poliakoff because Poliakoff has been busy working in TV. Unlike most scripts, which are a chore to read, Poliakoff's has the urgency of a mystery thriller - a quality that is all the more surprising when you look at his chosen subject of education. However, this is not a world of rebellious kids and assemblies held in halls with scuffed parquet flooring.

I never meant to be away from the theatre for so long

Set in contemporary London, it is mainly a nocturnal play in which its heroine, Lambert, a retired primary school teacher (a role that has enticed Tracey Ullman back on to the London stage), hangs out in some of the city's darkest and most dangerous corners. It's also a kind of memory play, patched together with Poliakoff's experiences as both a pupil and a father.

It begins when Richard, one of her former pupils from decades ago, meets her while she is lying on a park bench. It is a play that makes a plea for teachers to be valued much more than they are. In some ways the theme is a return to earlier urban plays in which the city and how children are moulded by the adults around them around them are prime concerns.

Sweet Panic, for instance, features stressed parents who strain every sinew to ensure their children are high achievers. These are perennial issues. But whether intended or not, My City - in which a teacher despairs of a world that her teaching has helped create - feels very now indeed in this post-riot era in which parents and teachers are asking themselves what went wrong.

"It could not be more apt for today," agrees Poliakoff.

The early years in education were not happy ones for Poliakoff. "I was the only Jewish boy at boarding school, this very old fashioned boarding school. I hated it. But I didn't hate all my teachers," he adds. Although when he talks about his education - from country boarding school to Cambridge, via Westminster - the early memories all seem bad.

"Boarding school - the fear, the sarcasm…" he begins. "There was a teacher with a wooden leg who you could hear clunking down the corridor and who would make the children touch it." A version of this real-life demon is in the play. And there are other demons, such as the Holocaust, a theme that Poliakoff often deals with, but with a unique subtlety that reveals the legacy of the Holocaust without delving into the experience.

But with My City the prime concern is a parental one - he has two children - and how schools deal with marginalised pupils. The other main character in the play is Richard (Tom Riley) who, when he was a child, was helped over his attention deficit issues by Ullman's character. Rather like Poliakoff, Richard was an outsider in school. Are there similarities between the Richard's and Poliakoff's school?

"I didn't have attention deficit", says Poliakoff anticipating the "is Richard you?" question. "But today I might well have… they might have tried to… normalise me," he says. "I know that I was regarded as an oddball."

When I ask what he puts this oddball-ness down to, we are off again on one of those replies that veers, stops, starts and this time takes a detour along some of that well documented though fascinating family history - the Russian father, the English mother from Jewish aristocracy, and less well known, how her family made enormous wealth as bankers and then lost much of it, and then the late age at which his parents had their children.

"My mother was 39 when I was born. So in a sense they were midway to being grandparents. Most of my contemporaries' parents are still alive and mine are long dead. Their formative years were the 1930s and I almost feel I was alive at that time."

And the war also? "Yes, they would have been among those who would have been rounded up." So is that what makes you odd?

"No. Well, I suppose all writers have eccentricities because it is an eccentric thing to do to sit alone in a room and write. And to have a long career doing that, you have to combine different things including self-belief, stubbornness, and obsessiveness. I think I have all of those," he says taking a first bite of his sandwich.