Angela Cannings, 40, from Salisbury in Wiltshire, was sentenced in April 2002 for the murder of seven-week-old Jason in 1991, and 18-week-old Matthew in 1999.

Ms Cannings has always maintained the two boys died of Sudden Infant Death Syndrome (SIDS), also known as cot death. SIDS was recorded as the cause of the death of her first daughter, Gemma, who died at the age of 13 weeks in 1989.

Ms Cannings has one surviving daughter, born in 1996.

Four-minute decision

The three judges took just four minutes to quash Ms Cannings' conviction after a five-day appeal.

During the hearing, the judges heard that Ms Cannings' relatives had also lost babies.

They were also given recent research suggesting the recurrence rate of SIDS after a prior cot death is almost six times greater than in a "normal" family.

The evidence discredited the controversial opinion of expert witness Professor Sir Roy Meadow that, unless proved otherwise, one cot death is a tragedy, two are suspicious and three are murder.

In delivering the verdict, Lord Justice Judge said not enough was known scientifically about the causes of cot deaths for juries to exclude natural causes of death in such cases.

"The door never seems to be closed to new views about what may or may not cause cot death," he said.

'Living hell'

After the conviction was overturned, Ms Cannings said, "These last four years have been a living hell.

"Finally today justice has been done and my innocence has been proved. I would like to go home now and be mummy to our very precious daughter."

This is the third case this year in which a mother accused of killing her babies has walked free.

In January, solicitor Sally Clark, given a life sentence for murdering her two baby sons, was freed on appeal after spending more than three years in prison.

And in June, 35-year-old pharmacist Trupti Patel was cleared of murdering her three babies by a jury at Reading Crown Court.

Sir Roy Meadow was also involved as a prosecution witness in these cases.

The government has ordered a review of the procedures used for investigating mothers accused of murdering their own babies.

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