A man was tonight still being quizzed by detectives over the murder of an Oxfordshire couple on holiday 20 years ago.

The bodies of Peter and Gwenda Dixon, of Moorlands Road, Witney, were discovered on a coastal path at a Welsh beauty spot in July, 1989. They had been shot dead.

Mr Dixon, 51, had his hands tied behind his back and his wallet was missing, while Mrs Dixon, 52, had had her clothes partially stripped off her.

Today, a Dyfed Powys Police forensic review team arrested a 64-year-old man in Letterstone, Wales, around 15 miles from the killing, on suspicion of the couple’s murder.

The man is also being held over the killing of another holiday couple in Wales 24 years ago and a robbery and sex attack.

Deputy chief constable Andy Edwards said: “Dyfed Powys Police have conducted a review of unsolved serious crimes committed in Pembrokeshire dating back to 1985.

“This investigation has been named Operation Ottawa. The offences include four murders as well as other serious offences.

“A local man has been arrested on suspicion of the murders of Helen and Richard Thomas at Scoveston Manor in December 1985, the murders of Peter and Gwenda Dixon on the Pembrokeshire coastal path in 1989 and a serious sexual assault and attempted robbery in Milford Haven in 1996.”

Mr Dixon, a former RAF lieutenant who worked for Buckinghamshire aerial firm Antiference, and his wife were on a camping holiday in Little Haven above St Brides Bay, Pembrokeshire, in June 1989.

Mrs Dixon worked at Yarnton House Community Centre as an administrative assistant.

Their son Timothy alerted police when they failed to return home from holiday.

He joined the search party on the clifftops and his parent’s bodies were found six days after they went missing.

Their haversacks and belongings had been strewn around a wooded area.

They had been killed with a shotgun. Witnesses told police they heard gunfire on the morning the couple left their campsite.

Days later a cyclist was seen using Mr Dixon’s bank card to withdraw £310.

Hundreds of mourners paid their respects at Our Lady and St Hugh’s Church in Witney.

Police took more than 10,000 statements, issued a £5,000 reward and filmed a reconstruction for Crimewatch.

Officers even investigated whether the couple were killed by the IRA after a smuggled arms cache was discovered near where they died and also travelled to France and Germany to investigate similar murders.

Nine years after the murder, police found a shotgun — believed to have been used in the murder — in a lake.

A 53-year-old man arrested over the killing was never charged.

An inquest in 1990 ruled unlawful killing.

Today, the couple’s children Timothy, 46, and Julie, 38, did not want to comment on the development.

Following the arrest police have 24 hours to question the man, but could apply for a further 12 hour extension today.