Three former Khmer Rouge guerrillas have been sentenced to 20 years in jail by a Cambodian court for the kidnapping and murder of a British mine-clearer and his translator 12 years ago.

A fourth man was jailed for 10 years for his part in the crimes. A fifth, Cheam Chit, 38, was released by the court after trial Judge Iv Kim Sri accepted that he had been forced at gunpoint to lead the rebels to the place where they could ambush Howes.

Christopher Howes and his translator Houn Hourth, who worked for the British charity the Mines Advisory Group (MAG) were kidnapped as they cleared mines near to the Cambodian temple complex Angkor Wat in March 1996.

For two years, as Pol Pot's regime spiralled into collapse, the fate of the former British army engineer from Backwell in North Somerset remained a mystery.

The remains for the victims were found in 1998, after the fall of the Khmer Rouge, and a Scotland Yard investigation found that Mr Howes had been killed three days after being abducted.

However it took another decade before five men were arrested and charged with his murder. Khem Ngun, Puth Lim, Sin Dorn, Loch Mao and Cheap Chet were also charged with the abduction and murder of Mr Houth and the kidnap of 20 other members of Mr Howe's team.

The five men denied taking any personal part in the killings of Mr Howes and Mr Houn, and blamed the crime on two other guerrillas who are believed to be dead.

The 20 other mine clearers kidnapped with Mr Howes were released after he agreed to remain with their captors as surety for a future ransom. But he and Mr Houn were shot dead within a week after being given a last meal of apples and the tropical fruit durian, Cambodian prosecutors told the trial.

The court heard that Mr Howes had been killed on the orders of Pol Pot because the communist leader had a blanket policy of killing foreigners on the grounds that they supported the Cambodian government. Mr Houth was murdered a day earlier when he was deemed "no longer necessary" because one of the accused spoke English.

One of the accused men, Loch Mao, told the court that his senior commander, Khem Tem, had ordered another soldier, Nget Rim, to kill Mr Howes.

"Howes fell backward. It was one single shot," said Mr Loch. "Khem Tem then ordered me to fire more shots. I walked up with the intention of firing a shot into his chest, but Khem Ngun yelled, 'That's enough, he is already dead'."

Mr Khem, who subsequently defected from the Khmer Rouge and was a major-general in the Cambodian Army at the time of his arrest last November, denied that he had ordered the shooting. He told the court: "Another Khmer Rouge soldier close to Ta Mok ordered the shooting of Howes in the head, and then I turned my face away and felt shock."

Another of the accused men, Put Lim, said that Mr Howes was killed at night and his body was cremated on a wood fire.

Mr Howes served seven years in the Royal Engineers before working for MAG in northern Iraq and then Cambodia. His courage in refusing to leave his co-abductees earned him a posthumous Queen's Gallantry Medal and King Noradom Sihanouk of Cambodia has named a street in the capital after him.

In 1996, MAG reportedly paid $120,000 to a man who claimed he could gain Mr Howes's release, but he then absconded with most of the money.

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