A mentally ill British man who stabbed a motorist to death after a minor fender-bender has cleared of murder but convicted of manslaughter on the grounds of diminished responsibility.

Matthew Daley knifed 79-year-old Donald Lock 39 times on a road in southern England in July after their cars were in a low-speed collision.

Daley's family told a jury at Lewes Crown Court in southern England that they had pleaded with doctors to take the 35-year-old into psychiatric care after years of mental-health problems.

Local health authorities have apologized for not providing better care.

The victim's son, Andrew Lock, said after Monday's verdict that "it is clear that dad would still be here today if they had done their job properly."

Judge Rabinder Singh set sentencing for July 8.