Mark Rowntree has been locked up at The Hutton Centre, a secure unit at St Luke's Hospital in Middlesbrough, since 1991.

Bizarrely, he feels justified in complaining about the conditions under which he is held.

"It's ostensibly a hospital, but it's like a little Colditz. It's a terrible rat-trap and I have suffered for 12 years. Patients are doing a long time - some don't get any fresh air for weeks on end," he said.

A decade ago there was much speculation that Rowntree was on the verge of being released. But he says his hopes of parole were ended after publicity about him being allowed out on day trips to the Kielder Forest adventure park in 1994 and to a pop concert in Middlesbrough four years later sparked an outcry.

"I haven't been out since."

Rowntree says he was recently transferred to the high-security ward at the centre because he was considered dangerous and suicidal.

"I've been treated very cautiously. I'm under five-minute observation, all day, all night. There's six staff on the ward and patients are smashing televisions, chucking cups about, pulling pictures off walls, slashing their wrists - and that's no exaggeration. It's a very disturbed acute ward. God knows what's going to happen to me."

However, he believes he will soon be transferred to a high-security establishment, either a prison or back to a secure hospital like Rampton or Ashworth.

In a chilling and calm manner, he reveals one reason why he expects to be moved is because he threatened to kill a social worker.

"She made some statements on a mental health tribunal hearing that I had no remorse, and it hurt me very badly. My mother was present and it shocked and hurt her and I can't seem to have forgiveness for the social worker. I made a threat to kill her and I said that I still would - and I'm sad to say that I still will. And if I can't I would pay someone to do it because I have inherited a lot of money."

He goes on: "I do not think I'll be released for reasons of gravity of my offences and I wouldn't wish to be released. I think I'd be very vulnerable to reprisals.

"The attitude towards people like me has not relented, in fact it's got worse."

At the time of the killings, Rowntree was a 19 year-old student living with his adoptive parents in a detached house in an upmarket area of Guiseley.

His parents are clearly still important to him and he speaks fondly of his mother's support.

"I am in touch with my mother. She's the only person in the world that I've ever cared for.

"She's never really got over it but she's had a mother's love for me and that's amazing. She knows what I've done. She knows I'll never be released, that I was hopelessly long-term, but she has never once admonished me because she truly loves me and she doesn't know what went wrong all those years ago."

Rowntree describes his childhood as "very happy" but says he was abused, bullied and teased at boarding school.

He had a religious upbringing but he says he has now lost faith and describes himself as feeling "angry with God".

Since being locked up, Rowntree gained an Open University degree in social sciences and sparked a furore when he won a book deal after writing a novel, 'The Reality Factor' - a semi-factual account of life in psychiatric units - written under the pseudonym Mark King.

Now he boasts about two more books he has written, 'Mirrors,' a collection of poems, and 60 short stories on science fiction, love and romance under the title of 'Imagination Avenue.'

Both are written under the pseudonym Alex Heaton - one of four different names he has used since being locked up. In the 90s he changed his name to Paul Page. Now he used the name Mark Evans.

It is clear that Rowntree is still an ill man - despite some of his protestations to the contrary.

At times he talks of his illness being under control but says it has never been identified. The only consistency is the calm and measured tone in which he speaks.

"I feel my illness is now well under control.

"I am prepared to admit now that I could be a bad man. For so long I have even kidded myself, assuaged my conscience, that I was mad, which appeased me.

"It may be the case that now I have matured I'm facing up to the fact that I was truly a rotten apple. I don't know if I'm curable or not.

"It frightens me because most people get a diagnosis and everyone knows, or is pretty sure, what the factors are. But in my case no-one knows, it's an unknown quantity after 27 years."