While Hertfordshire Oil Storage Limited was found guilty of failing to prevent major accidents and limit their effects. They also pleaded guilty to causing pollution to enter controlled waters underlying the vicinity around Buncefield.

The Health & Safety Executive and the Environment Agency said: "This was the biggest and most complex criminal inquiry we have worked on together - the product of many hundreds of hours of painstaking forensic investigation.

"When companies put workers and members of the public at risk and cause environmental damage we will prosecute.

"When the largest fire in peacetime Europe tore through the Buncefield site on that Sunday morning in December 2005, these companies had failed to protect workers, members of the public and the environment.

"The scale of the explosion and fire at Buncefield was immense and it was miraculous that nobody died. Unless the high hazard industries truly learn the lessons, then we may not be that fortunate in future."

Sentencing is due to take place next month.