Police have reopened an investigation into the unsolved murder of a taxi driver more than 40 years after his body was found in a field.

John “Jack” Amstrong, 58, went missing on October 5 1979 after picking a customer up from a pub in Cardiff, and his bloodstained taxi was discovered later that evening on an industrial estate in Bridgend.

His body was found three days later 11 miles away on Cowbridge Common having sustained catastrophic head injuries, but his killer was never found.

On Thursday, South Wales Police said its specialist crime unit was reviewing the case in the hope that advances in forensic science and a “change in loyalties” would help unearth how Mr Armstrong was killed and by who.

Detective Chief Inspector Patrick Catto, head of the review unit, said he hoped the new investigation could provide the taxi driver’s family with closure and justice.

He said: “No case is ever closed and we remain committed to periodically reviewing unsolved cases in the hope that advances in forensic sciences and technology will provide us with a new line of inquiry.

“The 1979 investigation was thorough and this review is no reflection on our colleagues who were involved at the time. We do, however, owe it to the victim and his family to make sure we exploit every scientific advance available to us to try and secure the breakthrough we need.

“If the killer is still alive, they’ve been living with the knowledge of what they did for more than 40 years. In addition, it’s likely that someone out there knows who did this, and people’s loyalties change.

“I’d appeal to anyone who believes they know the identity of the killer to come forward. Keeping such a secret will have been a heavy burden – it’s time to do the right thing and come forward.”

Anyone with any information which could assist detectives is urged to contact the review unit via 101, quoting occurrence 2000304349 or online at bit.ly/SWPReport.