Vanessa Arscott was killed moments after her boyfriend, Adam Lloyd

Adam Lloyd, 25, and Vanessa Arscott, 24, were killed on a night out near Kanchanaburi, 80 miles west of Bangkok, in the early hours of Thursday.

Ms Arscott was from Ashburton, Devon, and Mr Lloyd was from Northampton.

Police said an arrest warrant had been issued for their main suspect, police Sergeant Somchai Visetsingha, who had been missing since the shooting.

Policeman suspect

Reports say Ms Arscott was knocked down by a car and dragged for 20 yards after trying to stop the gunman who had shot her boyfriend dead.

She was shot dead too.

The couple were taken to Phahol Polpayuhasena hospital but died on the way there.

The couple are believed to have met their killer earlier in a riverside restaurant when he got involved in an argument which began when Mr Lloyd became upset at the way other customers were looking at his girlfriend.

He and Vanessa had been travelling together for two months. It was something he always wanted to do Linda Lloyd, Adam's mother

Police Colonel Vej Somboon said bloodstains had been found in the private car belonging to off-duty police Sgt Somchai.

He said witnesses saw the victims arguing with Sgt Somchai at the restaurant at around 2am.

He added that Sgt Somchai has been missing since the shooting and they hoped to catch him soon.

"The witnesses and evidence show that he is the man who gunned down the British tourists," he said.

'Lovely lad'

Mr Lloyd's mother Linda described her son as a "lovely lad".

She said: "He and Vanessa had been travelling together for two months. It was something he always wanted to do."

Mrs Lloyd, who runs the Buckingham Lodge Hotel in Torquay, Devon, with her husband Brian, said her son had been due to catch a flight home last week but couldn't get a flight.

Vanessa Arscott's grandmother Eileen Arscott, from Kingsteignton, south Devon, said: "I'm very distressed, the whole family is very upset."

She said her grand-daughter, who was studying health and fitness at college, used to stay with her at weekends.

Mrs Arscott said: "We were very close.

"She was due back this weekend. I cannot believe this has happened."

Ms Arscott's parents, who live on the edge of Dartmoor were too upset to comment.

Violent crime against foreign tourists is rare in Thailand, which lures 10 million visitors a year to its pristine beaches, temples and vibrant nightlife.

Thousands of tourists, many of them World War II veterans, also flock each year to Kanchanaburi, site of the notorious Thailand-Burma "death railway" and a Commonwealth war cemetery.

The bridge over the river was built by Allied prisoners of Japanese forces and immortalised in the 1957 film Bridge on the River Kwai starring Alec Guinness.

It was bombed during the war by Allied planes trying to disrupt Japanese supply lines.