A tanker driver who confessed to a friend that he fears he triggered the Buncefield oil depot blaze will be interviewed for a second time by police, it was revealed today.

As fire crews waited for the last serious fire - caused by petrol leaking from a ruptured valve - to burn itself out, the recovery operation and investigation into the cause of the 72-hour inferno began in earnest.

A worker at the plant near Hemel Hempstead told The Sun last night that a tanker driver believes he is responsible for the fire. He described how the man flicked the engine cut-out switch on his vehicle, causing a spark which may have ignited a heavy leak of fuel vapour.

"My colleague ran to his tanker, flipped the switch and waited. His engine cut out, then ‘boom!’ He does not know whether he caused it but he blames himself," he said.

Police confirmed that they had already questioned the driver and that he had presented a similar account to them.

At a press conference this morning Simon Parr, who is in charge of the police operation, said: "We know what that tanker driver has said, we are aware of his involvement and his activity on Sunday.

"Everybody who was on the site has been spoken to, and will be spoken to again as we build up a complete picture. We are speaking to this gentlemen."

He said, however, that it was too early to speculate, adding: "There are any number of possible causes."

Bob Woodward, of the Health and Safety Executive, said that investigators are focusing on the presence of a cloud of vapour witnessed in the plant moments before the explosion. It is unclear whether the gas escaped from one of the tankers as it was filling with fuel or from one of the 20 giant storage containers at the plant.

He said: "It is clear that there was a release of fuel, I believe this tanker driver was making reference to the sort of condition that could have started the explosion and fire.

"For an explosion you need fuel, oxygen and an ignition source. It's a question of finding what that [ignition] source was. It could be a number of sources either on site or off site. It would be difficult at this stage to pin this down. There are quite a number of possible causes."

Asked whether the tanker driver's report was among them, he replied: "Yes."

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