The grandson of Pat Regan, a campaigner against guns, knives and gang culture, was detained indefinitely today after admitting that he had killed her in a violent knife attack.

Rakeim Regan, 21, was said to have had a close relationship with his grandmother, who doted on him, but he suffered from severe paranoid schizophrenia which made him delusional, Leeds Crown Court was told.

Today, Regan denied murder but admitted manslaughter on the grounds of diminished responsibility. The prosecution accepted his plea and the judge ruled that he should be detained indefinitely at a secure mental hospital.

Regan had been taken to an accident and emergency unit after exhibiting bizarre behaviour on the night before the stabbing, but Mrs Regan asked for him to be returned home with her to her flat on Marlborough Grange estate, in Leeds.

He now admits killing her in a frenzied attack the following day. Regan also admitted wounding a railway manager with intent after he challenged a man for trespassing at the station.

Mrs Regan's anti-violence campaign, which started after her son was shot dead in 2002, led to her being courted by Cabinet ministers, praised by royalty and photographed with Tony Blair.

As a leading member of Mothers Against Violence, she took her message into schools, prisons and young offenders' institutions. She led street marches, gave interviews on radio and television, held one-to one sessions with worried parents and pleaded for more funding to support her work.

When news of her death emerged in June, Jacqui Smith, the Home Secretary, led the tributes, saying that she was shocked and saddened by Mrs Regan's death. "I had met Pat on several occasions and had been greatly impressed with her dedication to tackling gun crime," she said. "Her death is a great loss."

Judge Peter Collier QC heard that Mrs Regan suffered a series of stab wounds to her head and neck when her grandson attacked her in her home in Marlborough Grange, Leeds, on June 1 last year.

The court heard that Regan’s mental health had deteriorated in the early part of the year. In the days before the incident he had been arrested by police and after his release claimed officers had tried to rape him. He also claimed aliens were trying to get him, and that “reptilians” were all over the place.

Jeremy Richardson QC, prosecuting, told the court that, as the defendant became more delusional, he claimed his grandmother was a paedophile.

He was taken to accident and emergency at St James Hospital, in Leeds, on the night before the attack.

Regan was assessed by a mental health nurse who weighed up whether to release him with medication or to detain him under the Mental Health Act. But Mrs Regan asked for her grandson to come home with her.

Graham Hyland QC, defending, told the court: “It was Pat Regan’s wish for him to come home with medication. Tragically that wish, born out of her love and concern for the welfare of her grandson, cost her her life the following morning.”

After sentencing, Judge Collier asked whether health professionals could learn lessons for the future from the way in which Regan was dealt with at the accident and emergency unit.

He stressed he was not seeking to criticise anyone’s decisions and said “hindsight is a wonderful thing”.

But he urged health trusts to examine situations where families ask for relatives suffering from mental illness not to be detained.

He added: “It’s important to understand that those involved who made the decisions at the time were acting entirely properly.”

Times Recommends

• Milk: do we need a dairy godmother?
• DIY: the women doing it for themselves
• First double portrait of Princes unveiled