The detective leading the investigation into the murder of a wealthy businessman's wife 11 years ago said today that he was confident that new clues could still be uncovered.

Bikini-clad Ann Heron was sunbathing at her imposing home on August 3 the hottest day of the summer of 1990 when her throat was cut in what police believe to have been a sexually-motivated attack.

The body of 44-year-old Mrs Heron was found in a pool of blood by her husband Peter when he returned to the couple's home, Aeolian House, which stands in its own grounds on the outskirts of Middleton St George, near Darlington, County Durham.

Superintendent John Blake who as a detective sergeant worked on the investigation at the time of Mrs Heron's murder said today: "It is frustrating but I have to remain patient.

"There have been tremendous advances in DNA profiling in recent years which are still going on at a pace.

"While I do not want to raise false hopes, I remain confident the scientists will give us the vital lead we need."

Police have tried to trace the sun-tanned driver of a blue car, who was aged 35-40, which was seen travelling at speed down the drive of Aeolian House at about 5pm the time at which Mrs Heron is thought to have died.

Detectives have also appealed so far unsuccessfully for information about a male jogger wearing a blue vest and black tracksuit who was seen running in the area.

More than 1,500 items were taken from the crime scene and forensic scientists have re-examined a small number of them for minute clues.

Mr Blake said: "Over many months a great deal of work has been done and we are now focusing on just a handful of exhibits which will, I believe, ultimately yield that critical new piece of information we have been searching for."