Retired police chief Jim Marshall is calling for a change in the law following a child cruelty case.

He has written to Home Secretary David Blunkett after the death of four-year-old John Smith.

Simon and Michelle McWilliam, the boy's prospective adoptive parents, were each jailed for eight years on cruelty charges at Lewes Crown Court.

But as the law stands, they could not be tried with murder because they were the only people present when the little boy died.

Mr Marshall, former head of Sussex CID and Britain's longest-serving top detective, said: "This is not an isolated case as others are occurring both in our county and nationally."

He added: "The catalogue and variety of injuries shocked, appalled and saddened me beyond belief and I am a case-hardened detective."

Mr Marshall, a former Tory town and county councillor, said that there was no way of proving under current law who inflicted the blows that killed the boy.

He asked: "How could such injuries be inflicted by one person without another in the same house being aware of their origin?

"Quite clearly the law needs changing. Our children must be protected by a realistic deterrent."

Mr Marshall, a governor at Goldstone Junior School, Hove, for 20 years, campaigned for equal opportunities for children, especially those with special needs.

Mr Marshall's unique experience includes investigating the case of seven-year-old Maria Colwell, killed by her stepfather in Brighton in 1973.

He also served on East Sussex social services committee and the adoption panel.

Mr Marshall, a grandfather from Hove, has also taken up the issue with Hove MP Ivor Caplin.

Mr Caplin and Brighton MPs, David Lepper and Des Turner, are already pushing for a change in the law.

The Argus launched a campaign last year after a Brighton couple was convicted of cruelty to children. The pair could not be prosecuted for murdering three babies because the judge ruled there was no evidence to say which of them was responsible.

The then Home Secretary Jack Straw responded to The Argus by saying he was considering bringing in a new law of killing by cruelty which would carry a maximum 14-jail term.

Following the McWilliam case, The Argus editor-in-chief, Simon Bradshaw, wrote to the the new Home Secretary David Blunkett asking him to again review the issue.

A spokesman for the Home Office said the change was still being looked into.