At 56 Stephen Poliakoff is the undisputed heavyweight champion of British television drama. Now he has done something that he has never done before. He has made a thriller. Well ok, it is a thriller with many familiar Poliakoff ingredients — big houses, old money, and the English upper-middle classes.

But still, Poliakoff’s latest is a step away from the family sagas that he is normally associated with and for which he earned himself and the BBC a hatful of awards.

Set just before the outbreak of World War II, Glorious 39 is a proper thriller complete with fist-biting moments of tension. And it reveals how close this country came to being a puppet regime of the Nazis.

What is more, the writer/director wrote and directed it not for television, but for cinema. Why is this special? It is one thing to have earned the faith of BBC executives with stacks of awards and heaps of critical praise. But in these straitened times, it is quite another for this country’s tiny and tight-fisted film industry to stump up millions for a cinema release. This the power of Poliakoff. Though Poliakoff himself does not call it power. He calls it freedom.

“It was just £4 million,” says Poliakoff. “£4.3 million,” he qualifies. “Just under £4.3,” he re-qualifies. “£4.2. Call it £4.3.” Getting it right is important.

In chapel at his school, the boys would look to see if he would declare his belief in the father, son and holy ghost. He didn’t

We are sitting in his London office at TalkBack Productions, off Oxford Street. The walls are plastered with photographs of this country’s top tier of acting talent. There is Michael Gambon, who in Poliakoff’s TV film Joe’s Palace played a British billionaire whose wealth was connected to the Holocaust. There is Robert Lindsay in Gideon’s Daughter, Miranda Richardson and Bill Nighy in The Lost Prince, and next to the window are cast pictures of Glorious 39 — Nighy again, Romola Garai, Julie Christie, David Tennant, Christopher Lee… no wonder he got the funding.

Nighy plays the aristocratic patriarch of an influential Tory. Garai plays Anne, the first of his three children who was adopted into the family.

Glorious 39 takes its name from the perfect English summer before war broke out with Germany. Hitler was on the rampage, Chamberlain was in power, Churchill was a Prime Minister waiting in the wings. This much is generally understood. Less well-known is the extent to which the British establishment opposed war with Germany. And it is against this background that Poliakoff has written a story in which dark forces in England attempt to protect all they hold dear not by fighting Hitler, but appeasing him, even to the extent of killing British opponents of Chamberlain.

“The truth is that these people weren’t fascists,” says Poliakoff. “They feared Communism more and therefore either saw Hitler as not being too bad or the lesser of two evils. So that’s what I wanted to dramatise.”

His point is that although much of Britain’s identity is built upon the country’s opposition to Hitler, it very nearly did not turn out that way. In fact much of the imagery associated with the period — soaring Spitfires, a defiant Churchill, all the stuff that Nick Griffin’s BNP party has been attempting to appropriate — covers up the fact that much, if not most of the powers-that-be were hell-bent on avoiding war at all costs. And there is a scene, a sub plot, in Glorious 39 which quite brilliantly implies what that cost would be.

“A lot of people were evacuated and couldn’t take their pets with them, or down the shelters so they thought it best to have them put down,” explains Poliakoff. “So there was this extraordinary image outside the vets in high streets of piles of dead animals. When I read that, and an extraordinary quote from a New York correspondent about being in a city without children and without pets, I thought that was such a haunting image.”

In the film this image serves as a terrifying metaphor for what would have happened in Britain if the appeasers had had their way. “If they had done a deal, what happened in the rest of Europe would have happened here,” says Poliakoff.

It is not the first time a Poliakoff film has lifted the lid on the English upper classes and found something rotten inside. It could be said that most of Poliakoff’s work peels back respectable layers to reveal a disturbing truth. In his 1991 film Close My Eyes, starring Clive Owen, it was incest. In his 1999 play Talk of the City, it was the BBC’s record of reporting Jewish persecution in Nazi Germany.

Here, it is the establishment. And as the story of Glorious 39 unfolds, it is hard not to form the view that you are watching a film created by a someone with deep suspicion — antipathy even — towards the country of his birth.

The grandson of a Russian émigré who arrived in Britain at 14, Poliakoff was the only Jew at his Kent prep school. He remembers how during assembly in the “horrible little chapel” the entire congregation of boys would turn to him to see if he too would look at the cross and declare his belief in the father, the son and the holy ghost. He didn’t.

“Do I love the British establishment? A lot of people would say I was a sort of member of it. I certainly had a classic education, going to a country boarding school, public school and then Cambridge.” He did not finish his degree. The Hampstead Theatre was already putting on his work so he left university to become a playwright.

“I was brought up in very English landscapes. The prep school was a very beautiful house. It was very English, very army.” But he hated it.

“Yes. That is a very important point. I used to hate it. I was always aware of powerful dark forces. Maybe it’s all revenge. All my work is revenge. Maybe I’m a prep school martyr,” he jokes. But maybe he is. Glorious 39 is very much a film about the dark forces that run through the British establishment.

“I’m writing about the world that might have turned on me if I’d been alive a bit earlier and things had gone the other way,” admits Poliakoff.

“We don’t know how much resistance there would have been but we would definitely have gone the way of France. People still don’t quite believe that we would have collaborated.

“I think even though my English mum and my Russian dad were both Jewish, my dad was a terrific Anglophile. He loved Victorian architecture, he loved Rolls Royces. He was very enamoured with all the symbols of the British class system. I won’t deny that there is a sort of slightly outsider streak in my work. But I wouldn’t claim to be part of any other culture. I’m deeply embedded in it.”

Glorious 39 goes on release today