Police have seized a knife and sent it for forensic examination as they continue to question a man over the alleged road rage murder of a great-grandfather.

Donald Lock, 79, was knifed repeatedly after he got out of his car following a minor crash on the A24 at Findon, near Worthing, West Sussex.

Married for 55 years, Mr Lock, a veteran member of the Worthing Excelsior Cycling Club, died at the scene at around 8.40pm on Thursday.

His family said he had recently been given the all-clear from cancer and was due to become a great grandfather for the sixth time.

A 34-year-old man, from Worthing, is being questioned on suspicion of murder after he was arrested by armed officers some 18 hours later.

Sussex Police said they have seized a knife and are not looking for anyone else in connection with Mr Lock's death.

A post mortem has confirmed Mr Lock died as a result of stab wounds.

The senior investigating officer, Detective Chief Inspector Paul Rymarz of the Surrey and Sussex Major Crime Team, said: "Mr Lock was the victim of a violent, unprovoked attack that he had no chance to defend himself against.

"His family are devastated by his murder and are being supported by specialist officers.

"His family have requested that they are left to grieve and I would ask people to respect their wishes at such a difficult time.

"A significant number of officers are still involved with the investigation as we work to find out exactly what happened.

"This is a fast-moving operation and we are still looking for anyone with information contact us."

Police said Mr Lock was driving south on the A24 when he was involved in a minor collision with a car.

The driver of the first car then fatally stabbed the 79-year-old, got back into his car and drove away, police said.

Before he died, Mr Lock attended a social gathering of Worthing Excelsior Cycling Club, which stages a weekly evening 10-mile time trial in the summer, its secretary Adrian Palmer said.

The death devastated family and friends of Mr Lock, a Brighton and Hove Albion season ticket holder who still cycled up to 150 miles a week, relatives said.

In a statement, they said: "He still holds the club record for the 24-hour time trial having remained unbeaten for 44 years. He was full of energy having recently been given the all-clear from cancer.

"Not only was he passionate about cycling but he had also been supporting Brighton and Hove Albion since the 1940s and was a season ticket holder.

"He loved travelling the world with his wife Maureen and he adored his family. He and Maureen had just celebrated their 55th wedding anniversary."

Mr Lock, known as Don, leaves son Andy, daughter Sandra, four grandchildren, and five great-grandchildren, with the sixth great-grandchild due later this year. He had lived in Worthing for 55 years.

Anyone with information should call 101 quoting Operation Wise, email 101@sussex.pnn.police.uk or call Crimestoppers anonymously on 0800 555111.

A floral tribute left by Mr Lock's son, Andrew, read: "Forever in our hearts dearest dad. Now you are flying high with the seagulls. We will always look up to you. Miss you big time."