The film, Modern Times: Myra Hindley, asks "whether some crimes are so terrible that the people who commit them should die behind bars".

I could not bear the thought of being hanged. Although over the years I wish I had been

Myra Hindley

It features 150 letters she has written to the producer, read by an actress, telling the story of her meeting with Ian Brady and their relationship.

Hindley, who was sentenced to life in 1966 just after the death penalty was abolished, says in one letter: "I knew I was a selfish coward but I could not bear the thought of being hanged. Although over the years I wish I had been.

"It would have solved so many problems. The family of the victims would have derived some peace of mind and the tabloids would not have been able to manipulate them as they do to this day.

"I would have made a total confession to the priest before I hanged and would not still be half crippled by the burden of guilt that will not go away. But I didn't hang."

Hindley has studied for a degree in jail

Hindley described in her letters how the strength of her love for Brady had been part of the reason she allowed herself to be pushed into murder.

She described him has having "such a powerful personality, such an overwhelming charisma. If he'd told me the moon was made of green cheese or that the sun rose in the west I would have believed him."

The BBC has said the documentary is "important", despite outrage from the victims' families.

They have branded the film "a disgrace and an insult".

Alan West, whose daughter Leslie Ann was murdered by Hindley, said: "Why can't the families be spared the constant indignity of Hindley's continuous publicity seeking?"

Ian Brady was convicted of three murders

The families also feel they have been given less media coverage than Hindley and her accomplice Ian Brady over the years.

But BBC Director of Television Alan Yentob said the film complemented the national debate over the length of life sentences. He said it is the third time in three decades the BBC has "tackled the subject".

Hindley and Brady, the "Moors murderers", killed five children and buried their bodies on Saddleworth Moor, near Manchester.

In 1966, Hindley and Brady were convicted of murdering two children, 10-year-old Lesley Ann Downey and 17-year-old Edward Evans. Brady was also convicted of murdering 12-year-old John Kilbride.

They later confessed to two other murders - those of 16-year-old Pauline Reade and Keith Bennett, 12.

Executive producer Alex Holmes defended the programme, saying: "This film is not a platform for Hindley but an attempt to reach some understanding of the terrible crimes that happened.

"It's investigating whether life should mean life, an important and current debate that is going on.

Hindley, who lost an appeal against a ruling that she must spend her life in jail, has been dubbed "the most evil woman in Britain" by the press. But her supporters say she is a reformed woman.