A Saudi described as a spokesman for the group that kidnapped Bigley said two of his captors had accepted a large sum of money to help him flee after three weeks of captivity. The money was provided by a Syrian and an Iraqi who had penetrated the group on behalf of British intelligence, the spokesman claimed.

Bigley was bundled into the car last Wednesday and driven towards the safety of an area under the control of American forces near Latifiya, southwest of Baghdad, he said.

But after only five minutes the vehicle was halted by other members of the Tawhid and Jihad terrorist group.

The terrorists, who were patrolling the road in two separate cars, were from a different cell but recognised Bigley’s face and detained him, along with his companions.

They took the 62-year-old Liverpool engineer back to the house where he had been held, and he was beheaded on Thursday. His two helpers were also executed, the spokesman said.

The claim of an MI6 rescue attempt that backfired came from a man described by resistance fighters in Latifiya as the only person who could speak for the Tawhid and Jihad group. They gave his name as Abu Ahmad al-Saudi and his temporary address as a house in the village of Jars al-Sakher.

Speaking at the house, al-Saudi said Bigley had been generally well treated before he tried to get away, and had been given plenty to eat and drink. The Foreign Office refused to comment and Downing Street said it did not know if the claims of an escape were true.

An American official described them as credible and an Iraqi government source was quoted as saying that witnesses had reported seeing Bigley recaptured.

An Iraqi resistance commander with connections to Tawhid and Jihad later supported al-Saudi’s account. He said that when the group realised it had been compromised, it killed Bigley in the belief that its bolthole was about to be stormed.

According to an Iraqi cameraman who saw a video of Bigley’s last minutes, he was dressed in an orange jumpsuit and allowed to make a final plea for his life, saying: “I am a simple man. I don’t want to die.”

The cameraman said Bigley had reiterated that he needed his government’s help, adding: “Tony Blair has not done enough for me.”

A statement was read in Arabic by one of the captors, who complained of the British government’s failure to secure the release of Iraqi women prisoners held in American custody as the kidnappers had demanded. A man standing behind Bigley then beheaded him with a knife.

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