Mr Howes, from Clevedon near Bristol, was abducted in Cambodia more than two years ago and there has been no concrete evidence as to his fate since.
But according to a report in Time magazine, two former Khmer Rouge leaders have spoken about his death after defecting from the guerrilla organisation which is beset by in-fighting. Yim Panna and Ke Pauk reportedly claimed that Mr Howes was shot in the back, on the orders of Khmer Rouge leader Pol Pot himself, just one week after he was seized.
The pair said Mr Howes was shot near Anlong Veng, the Khmer Rouge's last stronghold, and his body was then burned.
A team from Scotland Yard, as well as Cambodian and Thai military intelligence, has carried out exhaustive inquiries into what happened to Mr Howes, without reaching a definite conclusion.
The Foreign Office said yesterday the report was the latest in a stream of unconfirmed stories. A spokesman said: "There have been a very large number of rumours surrounding Christopher Howes but so far there is no conclusive evidence to show what has happened.
"It remains a very high priority to establish the truth.
"We are in very frequent contact with the Cambodian government and any other sources we think may have relevant information."
Mr Howes' father said from his home in Clevedon yesterday that he regarded the Time magazine report with "scepticism".
He said: "I treat it with the same scepticism I treat all these rumours.
"The people the writer has got it from have already been questioned by the British ambassador in Cambodia. This report is just an elaboration of a story we have heard before.
"He has now been killed at about six different dates, places and in six different ways. Until I have absolute proof he is dead, he is alive and he has to be got out."
A Foreign Office spokesman said British embassy officials in the Cambodian capital, Phnom Penh, had "almost certainly" interviewed the two guerrilla leaders making the claims.
The report says Mr Howes' body was burned and then his bones were scattered over the ground. A tractor then reportedly cleared the bones, ploughing them into the earth in a rice field.
The claims were made by the two senior Khmer Rouge leaders during separate interviews.
Ke Pauk, 68, was commander of Cambodia's northern zone during Khmer rule 20 years ago and Yim Panna, 42, was a commander of Khmer Rouge division 980.
Yim Panna said of Mr Howes' death: "That was Pol Pot's rule. He didn't want any foreigners involved in our country."
Ke Pauk named Mr Howes' killer as a soldier named Bao. He said three other soldiers, Tem, Kong and Ngoun, were also involved.
The latest report comes in the wake of a long line of rumours that have surrounded the fate of Mr Howes since he disappeared in March 1996.
On 27 April 1997, a pounds 75,000 ransom was handed over to a man in Phnom Penh, against Foreign Office advice. The man had promised to secure Mr Howes' release. But nothing came of the promise.Reuse content