Sweeping changes to the handling of cases in which mothers are suspected of killing their babies were signalled yesterday by the court of appeal and the attorney general.

Hundreds of parents convicted of killing their babies will have their cases urgently reviewed, the attorney general announced, after the appeal court called for a halt to prosecutions of parents when expert opinion is divided on the cause of death.

Medical science was "still at the frontiers of knowledge" about unexplained infant deaths, said Lord Justice Judge, the deputy chief justice, giving the appeal court's reasons for its decision last month to quash Angela Cannings' conviction for murdering her two baby sons.

Where a full investigation into two or more sudden unexplained infant deaths in the same family was followed by a serious disagreement between reputable experts about the cause of death, and natural causes could not be excluded as a reasonable possibility, "the prosecution of a parent or parents for murder should not be started or continued unless there is additional cogent evidence".

The rethink, prompted by Mrs Cannings' case and those of Sally Clark and Trupti Patel, means prosecutions will be brought in future only where the evidence is much more clear cut.

A national protocol, to be drawn up by a working party chaired by the Labour peer and criminal QC Helena Kennedy, will ensure that these difficult cases are investigated as expertly as possible from the beginning. Police are represented on the working party, set up by the Royal College of Paediatrics and Child Health and the Royal College of Pathologists.

The attorney general, Lord Goldsmith, who oversees the Crown Prosecution Service, said the judgment had "serious and far-reaching implications", and he shared the unease expressed by the court of appeal.

He told the House of Lords: "The judgment has demonstrated that, in relation to unexplained infant deaths, where the outcome of the trial depends exclusively, or almost exclusively, on a serious disagreement between distinguished and reputable experts, it will often be unsafe to proceed."

Before Mrs Cannings' appeal, the cases of the solicitor Sally Clark, whose conviction for murdering her two baby sons was quashed on the second appeal, and pharmacist Trupti Patel, acquitted of the murder of her three babies, had already highlighted the uncertainties faced by experts in determining the cause of death when babies die suddenly.

Evidence from one prosecution expert, the retired paediatrician Professor Sir Roy Meadow, was a key factor in each case. Known for espousing the controversial rule of thumb that "unless proven otherwise, one cot death is tragedy, two is suspicious and three is murder", he proved a compelling witness in each case.

But yesterday Lord Justice Judge said that although the court recognised that three sudden infant deaths in one family was "very rare or very rare indeed", the fact that they occurred did "not identify, let alone prescribe, the deliberate infliction of harm as the cause of death".

The 258 cases to be reviewed are all those in which a parent has been convicted within the last 10 years of murder, manslaughter or infanticide of a child under two. Many will be cases where the evidence of guilt is clear cut - where, for example, a brutal father has battered a baby to death - but those where sudden explained death is a possibility will be identified for possible appeals.

Of the 258, the 54 in which parents are in prison will be given priority. The Criminal Cases Review Commission (CCRC) said it expected the number of cases sent to it to be "significantly lower than the headline figure of 258".

It added: "Such cases are likely to involve a number of causes of death and a variable level of expert involvement and it will be important to identify those where expert witnesses were crucial to securing the conviction."

Lord Justice Judge, sitting with Mrs Justice Rafferty and Mr Justice Pitchers, said: "In cases like the present, if the outcome of the trial depends exclusively or almost exclusively on a serious disagreement between distinguished and reputable experts, it will often be unwise, and therefore unsafe, to proceed. We recognise that justice may not be done in a small number of cases where in truth a mother has deliberately killed her baby without leaving any identifiable evidence of the crime. That is an undesirable result, which, however, avoids a worse one.

"Unless we are sure of guilt, the dreadful possibility always remains that a mother, already brutally scarred by the unexplained deaths of her babies, may find herself in prison for life for killing them when she should not be there at all. In our community, and in any civilised community, that is abhorrent."

Lord Goldsmith will meet the CCRC chairman this week to discuss how to expedite the case review. He has also asked the CPS to review the 15 ongoing prosecutions where there is a conflict of medical evidence and sudden infant death syndrome could be a possibility.

Mrs Cannings, 40, a shop assistant from Salisbury, Wiltshire, was convicted in April 2002 of smothering seven-week-old Jason in 1991 and 18-week-old Matthew in 1999. She was not charged over the death of her first child, Gemma, at the age of 13 weeks in 1989. Her surviving daughter, who cannot be named for legal reasons, was born in January 1996.

Speaking outside court, she said: "We are just glad it's all over and we can be reunited as a family."

Question mark over verdicts

· Donna Anthony, 30, from Yeovil, Somerset, who is serving life at Durham prison, has already filed an appeal against her conviction for the murder of her two babies, 11-month-old daughter Jordan in 1996 and Michael, four months, in 1997. Professor Sir Roy Meadow told police the death of Michael, who had respiratory difficulties, was typical of a smothering case "right down to the smallest detail"

· Margaret Smith, 38, of Hull, was jailed last year for life for smothering her son, Keith, four months, in 1994 after an eight-year-old girl gave evidence that she had seen her do it. She was cleared of murdering her daughter, Kelly, five months, in 1992

· Julie Ferris, 31, a mentally ill mother from Birmingham, was found to have smothered Hayley, nine months, in 1993 and Brandon, eight months in 1997. She was bailed last May pending a retrial. Professor Meadow said there were "clear markers" of deliberate choking

· Maxine Robinson, 35, of Chester-le-Street, Co Durham, was jailed for life in 1995 for murdering five-month-old Anthony and 19-month-old Christine, who died together. A Home Office pathologist who examined the bodies said the deaths were consistent with suffocation, while other experts said the deaths were natural. An appeal was unsuccessful