It is a truism that writers mine their childhood for material. Dennis Potter was no exception: remember the palm-sweating scenes in the village school in The Singing Detective when the threat of punishment hung over a class of red-kneed boys and girls in hand-me-down cardigans? Potter, who was born in 1935, repeatedly returned to the 1940s and 1950s for inspiration. He experienced the war through children's rumours and the whispers of adults in the Forest of Dean.
Blue Remembered Hills is revived at the National Theatre while the world watches Potter's last works, Karaoke and Cold Lazarus on television. This too was first seen on television (in 1979) and caused a stir because all the seven-year-old characters were played by adults. Nevertheless, Potter himself described it as his most naturalistic work. It is certainly an unflinching study of the terrors and unrelenting cruelties of childhood, all the more disturbing because the rosy-cheeked torturers remain vulnerable and even innocent. There are also moments of convulsive hilarity.
The director, Patrick Marber, is, like the cast, too young to remember the war years, but he does not regard this as a disadvantage. Blue Remembered Hills is, he says, a universal story.
No adult characters appear. Among the "children", Willie is cleverer than Peter, but Peter is stronger. Raymond's stammer is routinely mimicked, Donald (nicknamed Duck, which he hates) is traumatised by parental abuse. Audrey and Angela, the only "girls" in the group, ape their elders, flirting or squealing for help when it suits them, but just as often taking charge like bossy mummies.
The war is both ever-present (fathers go missing; an escaped Italian prisoner is their bogey man) and as mythical as any other playground confrontation. Ingenious ways are found to eke out resources - squirrels' tails and jam jars can be turned to profit - but otherwise play goes on. The boys are painfully aware of the pecking order and two fight for position during the play; Angela, being pretty, has a different status from plain Audrey. Their playground is a forest, Potter's Forest of Dean, but there is nothing enchanted about it. Marber says that "the dramatic shadow of war hangs over the forest; they want to grow up to be killers".
The cast visited the Evacuees exhibition at the Imperial War Museum to get the period in perspective, but Marber has not asked them to do any other research. He has expected them to dig deep into their own experience, starting on the first day of rehearsals with an account from each of the best and worst moments of their childhood. "They would be more open now," he says, weeks later. "There is a difference between creating the illusion of childhood and being children. "
After all, Marber goes on, once you become adult, you can no longer observe children as they are when there is no adult present. "People have sentimentalised the piece; it is not a sweet story of children playing in the Forest. It is tough - but funny too."
And, ultimately, it is tragic. Poor Donald Duck, whose father is missing and who is regularly beaten at home does not survive. "Donald Duck," says Marber, "is a mechanism. They have to have a victim so that they feel better about themselves."
For the cast the intensity of childhood is exacting. "It is like playing verse drama," says Marber. "You are taught to think on the line in Shakespeare. A child expresses himself on the thought. What is most difficult for the actors is that they must remain raw and vulnerable for the duration of the piece. Usually, it's not long before an actor has the relief of a gin and tonic or a bit of wry sophistication." Not this time.
Blue Remembered Hills is in repertoire at the National Theatre (Lyttelton) 0171 928 2252; Evacuees is at the Imperial War Museum, 0171 416 5000 Richard III (15)