The mother of a teenager who hanged himself in jail has demanded an inquiry into how prison chiefs administered the 18-year-old's medication.

Mark Hutton, who was battling to come off Drugs and suspected he might be HIV positive, hanged himself from a window handle in the middle of the night.

He was on remand at Doncaster Prison after raiding a card shop in Bingley at knifepoint last July and snatching £50 to feed his drug habit.

His mother, Christine Hutton, a 53-year-old nursing assistant from Keighley, believes her son could be alive today if he had been given tranquillisers later in the evening.

She said: "It was written down on his drug chart that he should have been given the medication at 9pm. He was given it at 6pm.

"It would mean he woke up earlier than he should and he would have had more time to become anxious and agitated before he was seen in the morning. I work in the health service and I know how important it is to have the drugs at the right time."

Mark was on a detoxification programme and was prescribed two drugs, including Diazepam, a tranquilliser, said Mrs Hutton, whose husband Robert, 49, is also a nursing assistant.

"The system at Doncaster needs changing. There must be something wrong that so many young boys are killing themselves," she added.

The private prison - dubbed Doncatraz because it is surrounded by water - has come under fire for the number of inmates taking their own lives since it opened in 1994. Five prisoners died last year, making it among the top three jails for suicide.

Doncaster coroner Stanley Hooper, who is this week hearing evidence about four deaths, recorded a verdict of suicide in Mark's case. The inquest heard that the detoxification course seemed to be working and Mark was in good spirits with prison staff and inmates before his death.

Ruth Bundy, who represented the family at the inquest in Doncaster on Tuesday, said she would be writing through Keighley MP Ann Cryer to the Minister for Prisons calling for an inquiry into the deaths and particularly about the administration of the medication.

She said Mark should have had his medication at 8am, 3pm and 9pm but it had been administered at 7.30am, noon and 6pm.

"He was medication free for 13 hours, which is a critical period for somebody who is depressed and worried," she said.

A spokesman for Premier Prison Service, which runs Doncaster, said: "We can't discuss the case until the inquests are over."

They were due to finish today.

Mark had not lived at home for two years and had no permanent address but the family, including his two sisters, Sharon Cook, 28, and Michelle, 21, kept in regular touch.

Mrs Hutton said he started sniffing liquid paper as a 14-year-old and his drug taking got gradually worse until he was on heroin and cocaine and sharing needles.

Drugs changed his character and he turned to theft to feed his habit.

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