The sergeant gave himself up after almost a month on the run

"He spat in my face, so I lost my temper and shot him," Sgt Somchai Visetsingha told Reuters press agency.

Mr Somchai, 39, has been accused of murdering Adam Lloyd, 25, from Northamptonshire, and Vanessa Arscott, 24, of Devon, on 9 September.

The couple's families thanked the Thai authorities following the arrest.

Run over

Mr Lloyd was last seen arguing with Mr Somchai at the officer's restaurant in Kanchanaburi, Thailand, reports say.

Witnesses said Mr Lloyd was shot and the killer then chased his girlfriend in a car, running her over and shooting her too.

Mr Somchai spoke about the case following an interrogation at Kanchanaburi police station after handing himself in.

He was reported as saying: "I think I fired all five bullets in my pistol's chamber."

He added he was not aware that he had killed Ms Arscott, the agency said.

"I meant to kill the man, but it [the car] accidentally hit her. I feel devastated that my good intention has turned out like this," he said.

'Difficult time'

Vanessa Arscott was killed moments after her boyfriend, Adam Lloyd

On Thursday, Mr Lloyd's brother Matthew said in a statement: "On behalf of the family I would like to thank the Thai authority for all the efforts they have made in capturing the man believed to be responsible for the murder of my brother Adam and his girlfriend Vanessa."

"As you can imagine it has been a very difficult time for us in coming to terms with our loss, " he said.

"I now hope there can be a swift trial and a quick result as I believe this will continue to help my family to come to terms and heal our loss," he added.

Ms Arscott's family said in their statement: "We know that the Thai authorities, particularly their police, have been working very hard over the past month."

"All we want now is justice for our darling Vanessa and also dear Adam and we have respect and confidence in the Thai justice system," it said.

Reward offered

Mr Somchai handed himself into police near the Burmese border on Thursday.

He was flown from the border by military helicopter to Kanchanaburi police headquarters.

On Thursday, he was expected to take part in a crime reconstruction at the scene.

BBC correspondent Simon Montlake said Mr Somchai was a respected policeman in the area.

British diplomat Andy Pearce said: "It was very difficult for the police to find him. It's to their credit that they followed it through in this way."

In mid-September, police had said Mr Somchai contacted relatives and friends saying he wanted to surrender.

Intensive search

Police had been conducting an intensive search for Mr Somchai for nearly a month, with a reward of 100,000 Baht (around �1,350) offered for help in his capture.

The Kanchanaburi province is about 70 miles west of the Thai capital, Bangkok.

The area attracts many foreign tourists because it is the site of the infamous bridge over the River Kwai, where Japanese troops forced prisoners of war to build a bridge during World War II.