A new law to prevent child killers escaping justice has moved a step closer.

An NSPCC working party has been meeting to finalise changes expected to be put to the Home Office later this year.

It has been studying cases, including two in Sussex, where guardians of battered and smothered children have escaped prosecution for murder because it cannot be proved which of the two was responsible for the fatal injuries.

The Argus, backed by families of children killed, has been campaigning for a change in the law for the past two years.

One 72-year-old man whose four-year-old grandson was battered to death welcomed the news.

He said: "It won't bring my boy back but this is great for the protection of children in the future."

Detective Inspector Malcolm Bacon, who investigated both Sussex cases, is on the NSPCC working party.

He said: "The cause has been championed by The Argus and I am more confident than ever a change is on the way.

"The working party will be putting forward realistic proposals that will be seriously considered by the Government. The proposals will enhance laws to identify guilty parties."

One idea will be a new law of killing by cruelty, something the Home Office is already considering. The new offence would carry a maximum 14-year prison sentence.

An NSPCC spokeswoman said: "We are concerned about cases where a child is killed or seriously injured and there is not enough evidence to say which parent or carer committed the crime.

"The result is that no one is held responsible."

The NSPCC group, working under the title Which one of you did it?, comprises a circuit judge, a Cambridge professor of criminal law, a consultant from the Royal College of Paediatricians, representatives from the Crown Prosecution Service, Mr Bacon and Sussex Police Detective Superintendent Steve Scott.

The Argus launched its campaign after a Brighton couple was acquitted of murdering three babies when the judge ruled there was insufficient evidence to say which parent was responsible.

Experts testified the babies had been smothered and the mother blamed the father, saying the children were crying and deserved it.

The same ruling blocked the prosecution for murder of Simon and Michelle McWilliam, from Fishersgate, Southwick, whose four-year-old adoptive son John Smith died after suffering 54 injuries including adult bites.

They were jailed for eight years each for cruelty. The couple are appealing against their sentences.

John's aunt, Linda Terry, 41, is lobbying MPs to close the "legal loophole".

She said: "We want to do everything we can to stop this happening again."

John's 72-year-old grandfather James Sweeney, from Hove, is continuing to deliver lobbying letters to local shops.

He said: "I will carry on fighting for as long as I live to stop these killers hiding from justice."