A woman who brutally and callously battered her grandmother to death with a spade for her money has been jailed for at least 20 years.

Joanne Hussey, 33, repeatedly struck 77-year-old Annie Garbutt, who had Alzheimer's Disease, as she lay in bed - then invented a story about voices in her head urging her to do it.

Judge Scott Wolstenholme yesterday told Hussey there had been a considerable degree of pre-meditation to the murder and she had then tried to cover her tracks.

The judge said: "You took a garden spade from your home and used it in a most brutal attack on your grandmother as she lay in her bed. You struck forceful blows with the spade repeatedly to her head, neck, upper body and limbs and continued to strike her when she tried to defend herself.

"At some stage it is clear you were sitting or kneeling on her. The multiple injuries you inflicted led to her death at some time during the night. She must have suffered greatly before losing consciousness.

"You then took considerable care to remove evidence that might connect you with the killing."

Hussey, of Grange Mount, Yeadon, who has a severely disabled 11-year-old daughter, was convicted by a jury at Leeds Crown Court last month of murdering her grandmother and brought back for sentencing yesterday.

The trial had been told that Mrs Garbutt's dementia had deteriorated and social services wanted her moved into full-time care. But Hussey feared her grandmother's considerable savings and investments would be swallowed up by the bills.

Postwoman Hussey, who had a string of affairs with fellow Royal Mail workers, attacked her grandmother at her terraced cottage home, in The Clough, Mirfield, in May last year. The pensioner suffered facial fractures, internal head injuries and fractures to her larynx, ribs and breastbone.

Judge Wolstenholme said yesterday there was no doubt Hussey was suffering from mental illness at the time of the murder, and was not taking her prescribed medication, but the seriousness of the offence was particularly high.

He told her: "The evidence does establish beyond reasonable doubt that you did expect to gain as a result of your grandmother's death.

"You would not have inherited any money from her, as you knew, because she had not made a will, but your mother would have succeeded to her entire estate."

The judge said her grandmother's money would be available to help pay for the care of her daughter if she lost her job on medical grounds.

"The expectation of that gain was a primary motive for this murder," he added.

"It's clear you wanted your grandmother's money to be available for your, and your mother's, use. You began to contemplate your grandmother's death as a way out of that dilemma."

He said the sentence for murder was fixed by law as life imprisonment. The appropriate minimum sentence she must serve was 20 years, less the 397 days she had already spent in custody, before the Parole Board could even consider if it was safe to release her, he added. Blonde Hussey held her head in her hands, then stared ahead as she listened to the sentence.

Judge Wolstenholme said Hussey had shown no remorse and when she realised she would be proved to be the killer she concocted a bogus defence of diminished responsibility with false claims to have heard voices urging her to kill her gran.

After the case, Detective Superintendent Andy Brennan, who led the investigation, said it was an appropriate sentence for a brutal and callous crime.

He said Hussey was an accomplished liar who for days brazenly denied any involvement in her grandmother's death.

Det Supt Brennan added: "Annie Garbutt was brutally killed because Joanne Hussey was motivated by greed. The attack and the financial motivation were something that books are written about. It is rare for us to come across them in reality."

Joanne Hussey was snared after police examined footage from Bradford's CCTV system which had caught her car on camera making the journey between her home in Yeadon and her grandmother's home in Mirfield four times during the night of Mrs Garbutt's death.

When first questioned by police the next day Hussey insisted she had spent the previous evening at home, gone to bed early and turned up at her grandmother's house that morning and found her dead.

But her account did not tally with the sightings of Hussey's journey on Bradford's Big Fish car checking camera system and, with their suspicions aroused, police began intensive forensic examinations at Hussey's home.

They found a tiny drop of blood from a spade which had a positive match to Annie's blood.

She was arrested on suspicion of the murder that evening and charged three days later after the spade was found in her garage and, after forensic tests, found to be the murder weapon.