Holdsworth, 37, a mother-of-two who has spent three years behind bars, was driven away from Low Newton prison in County Durham with a blanket over her head.

Lord Justice Toulson, Mr Justice Aikens and Judge Michael Baker QC granted her conditional bail after ordering a new trial over the death of her neighbour's two-year-old son, Kyle Fisher.

At her Teesside Crown Court trial Holdsworth was accused of repeatedly banging Kyle's head against a wooden banister.

She was said to have "snapped" while minding Kyle at her home in Millpool Close, Hartlepool, while the child's 19-year-old single mother was having a night out.

Holdsworth has consistently denied injuring the child and claimed he had suffered a fit as they sat watching television.

The prosecution case was that the boy died from a fatal brain swelling, or oedema, caused by a blow or blows of significant force. Jurors heard that the impact on his head was similar to being thrown from a car at 60mph.

Kyle, of nearby Troutpool Close, was rushed to hospital after the injury in August 2004, but died two days later.

During her appeal, which was opposed by the Crown, Holdsworth's QC, Henry Blaxland, told the three judges that the doctors who gave evidence at trial "got it wrong" and "collectively failed to diagnose" that the child had a "highly unusual brain", with abnormalities which predisposed him to epilepsy.

Overturning her conviction, Lord Justice Toulson said it was the court's view that if the fresh medical evidence had been given at trial it might reasonably have affected the jury's decision to convict.