THE killer of Darlington grandmother Sybil Sibthorpe was today jailed for life as a judge branded him "a significant danger to the public".

Lee Grainger senselessly battered the 80-year-old to death close to a house she owned and rented out in the town's Haughton Road on May 8.

Unemployed Grainger, 41, admitted the pensioner's manslaughter on the grounds of diminished responsibility at a court hearing last month.

The court heard how he had a personality disorder and was also impaired by "substantial and serious" head injuries suffered in an accident.

He was badly hurt when a motorbike he was riding smashed into a wall, which left him with an inability to exercise judgement and control.

Teesside Crown Court heard that he attacked his former landlady Mrs Sibthorpe after "brooding" for weeks about losing his tenancy.

Her body was found in the back yard of the property and police launched a murder hunt, saying she was the victim of a "sustained assault".

Grainger, of Elmfield Street, Darlington, was arrested at the scene, and told detectives: "Not murder, that's the worst type, isn't it."

He was due to go on trial for murder last month, but prosecutors were forced to accept a guilty plea to the lesser charge of manslaughter.

Two independent experts said in reports that he was suffering from an abnormality of mental function - a recognised medical condition.

Prosecutor, Jamie Hill, QC, said: "The defendant was substantially impaired . . . it provides a significant explanation for his actions."

Grainger's barrister, Nicholas Lumley, QC, said: "He accepts, and has always accepted, responsibility for the tragic and pointless death."

Judge Simon Bourne-Arton, QC, ordered that Grainger serve a minimum of 12-and-a-half years behind bars before being considered for release.

He said the killer had "acted out of a misplaced sense of grievance" and told him: "It is clear to me that you are a dangerous man.

"It is equally clear to me, if you were at liberty, you would continue to be a substantial risk to the public - a risk of unprovoked serious violence."

After this afternoon's case, Mrs Sibthorpe's family released a statement through police, describing her as "a peaceful, hardworking lady".

It said: "Our cheerful home is now cold, soulless, empty and silent without her. No-one will ever understand the pain that has been inflicted on our family when she was taken away from us in the most cruel, evil and scary way.

"She was a peaceful, hardworking and very talented lady who we all miss very much."

Detective Chief Inspector Steve Chapman paid tribute to the investigation team and lawyers for securing a conviction.

He said: "The sentence will be of some comfort and give the family a degree of closure, who have had a harrowing time since May."