A former binman who killed his girlfriend, her twin sister and an elderly couple was facing life behind bars last night after pleading guilty to murder.

Police believe Mark Hobson would have carried on killing had it not been for a member of the public who recognised him at a petrol station on the A19 near York.

Hobson killed girlfriend Claire Sanderson with a hammer before luring her sister, Diane, 27, to his flat a week later, where he sexually mutilated her. Hours later, he stabbed and killed James and Joan Britton at their home in Strensall, near York.

Leeds Crown Court was told yesterday that Hobson had no recollection of killing 80-year-old Mr Britton or his 82-year-old wife, and could offer no motive for the murders.

But the court was told the twins' killings had been pre-meditated. Police found about 100 handwritten notes at Hobson's flat, in Camblesforth, near Selby, North Yorkshire, which revealed he intended to kill Diane Sanderson.

References were also made to the twins' parents, George and Jacqueline, which suggested they were also his intended victims.

Paul Worsley, QC, prosecuting, said Hobson 35, had a disturbing history of violence, he regularly binged on drink and cocaine and, in the run-up to the deaths, was a user of gay and straight sex chatlines.

Claire, who had been dating Hobson for about 18 months and lived with him in Camblesforth, had been hit over the head 17 times with a hammer before a bin liner was placed over her face. By the time she was discovered, the body was so badly decomposed she could only be identified by her fingerprints.

Mr Worsley said that a week after killing Claire, Hobson lured Diane to his home, saying Claire had glandular fever. Diane was subjected to sustained blows and a "macabre and bizarre" sexual attack.

The twins' father was driven to attempting suicide by the trauma of their deaths and his discovery of their bodies at the flat on Sunday, July 18, last year. The same day, Hobson, high on a cocktail of cocaine, Ecstasy, alcohol and cannabis, walked into the Brittons' home and attacked them with a knife.

He left the house and went on the run, before being arrested near a service station in Shipton, North Yorkshire, after police were alerted when the owner recognised him.

There was evidence that he had tried to take his own life.

Yesterday, Hobson spoke only to plead guilty to the murders.

Prosecutors said they would be arguing Hobson should receive a whole life sentence, ensuring he is never released.

Jeremy Richardson QC, for Hobson, said representation would be made on his behalf at a sentencing hearing on May 27.

In a statement, the Brittons' daughter, Catherine Wilkins, who lives in Durham, said: "The needless and horrific violence inflicted upon them will be with me and my family for the rest of our lives."

Mr and Mrs Sanderson said: "They were our life, the reason we lived and worked. Now they are gone, we have nothing. They came into this world together and left it so tragically together.