Evil Simon and Michelle McWilliam, who subjected a four-year-old to systematic cruelty which led to his death, today lost a bid to cut their jail sentences.

The couple were jailed for eight years in October 2001 for an appalling catalogue of cruelty meted out to their adopted son John Smith. It left him with injuries likened to those on a battered boxer.

The McWilliams, formerly of Gardner Road, Fishersgate, Southwick, were granted leave to appeal earlier this year.

At London's High Court today Mr Justice Hughes and Mr Justice Royce said while they agreed the sentence was at the top end of the scale for cruelty they could see no reason for reducing it.

John's grandfather, James Sweeney, 52, welcomed the judges' ruling, saying: "They should have got 14 years for what they did. I'm over the moon they have not been let out early.

"I go to John's grave every week with a bunch of flowers and talk to him. Nothing will ever bring him back but hopefully we can start putting it behind us now."

John died on Christmas Eve 1999 with injuries including 54 bruises, three adult bite marks and burns to his face.

He had been living with the McWilliams since June 1999 but, despite months of abuse, social services failed to step in.

Simon McWilliam, 42, and his wife, 36, were charged with murder but the charge was dropped because each blamed the other for inflicting the fatal blows.

Sentencing them at Lewes last year, Judge Anthony Scott Gall said: "You systematically set about abusing that little boy, who wanted no more out of life than to be loved and to give love. You made a mockery of those wishes."

Peter Forbes, representing Simon McWilliam, today told the appeal court the sentence was too long as his client had not been charged with murder or manslaughter.

Andrew Bajwa, Michelle McWilliam's solicitor, claimed there was no evidence she had abused John, only that she had neglected him.

During the trial the couple alleged John had inflicted the injuries on himself.

Announcing his judgment after a 45-minute hearing, for which the couple were not present, Mr Royce said: "While it is correct to say that a sentence of eight years was at the top end, we are not persuaded that it would be right to interfere with the sentence."

Mr Royce described the facts of the case as "harrowing" and said it remained unclear who caused the fatal injuries.

Detective Inspector Malcolm Bacon, who led the police investigation, welcomed today's ruling.

He said: "This is an excellent result from the Court of Appeal. It reflects the seriousness of the offence and the actions undertaken by the McWilliams.

"It was a shame we could not convict them of murder but hopefully, with the inroads we are making at the moment, that could change in future cases."

Today's appeal came as Sussex Police and the NSPCC launched a report calling for a shake-up in the way child deaths involving more than one parent or carer are investigated and prosecuted.