A £5m government trial of schemes to divert mentally ill offenders into treatment rather than prison has been welcomed by campaigners.

The creation of 100 “diversion sites” was announced by justice secretary Ken Clarke and health secretary Andrew Lansley at a Women’s Institute function.

The WI has led a “care, not custody” campaign for three years after the death in Manchester prison of a Norfolk WI member’s mentally ill son.

A prison service survey published in November revealed that 12 per cent of inmates had a mental illness or depression as a long-standing illness.

Mr Clarke set out plans to introduce a national service by 2014 in a green paper last year as part of his wider shake-up of sentencing policy.

“Each death in custody is a tragedy for all those involved,” Mr Lansley said.

“We are taking active steps to improve the mental health and wellbeing of offenders, ensuring they get the same quality healthcare services in prison as they would in the community.

“Ensuring the health needs of offenders are identified promptly will help the police and courts to make informed decisions about charging and sentencing.

“But we also need to ensure that the right treatment is available.

“We know early intervention and prevention is essential and that more needs to be done to divert offenders with mental health problems away from prison and into community-based health treatment.

“That is why we’ll be modelling best approaches to this by putting £3m into up to 40 diversion sites for adults and £2m for up to 60 sites for young people this year. We believe that this will provide the foundations of better care and support for offenders.”

WI chair Ruth Bond said the commitment was welcome but put ministers on notice that the organisation would be watching to ensure it was backed by “sufficient political might”.

Juliet Lyon, of the Prison Reform Trust which co-sponsored the Westminster event, said: “When a highly respected organisation like the WI looks at the dark, neglected world of prisons and highlights the plight of people who are mentally ill then things start changing for the better.”