Total, the French oil giant, is facing a bill of hundreds of millions of pounds after a judge today found it responsible for Britain's biggest peacetime explosion.

The company was sued for about £750 million by insurance companies, other oil groups and hundreds of local residents following the fire at the Buncefield storage depot in Hemel Hempstead, Hertfordshire in December 2005.

Yesterday Mr Justice David Steel, sitting in the High Court in London, found that Total's UK arm had been negligent in failing to prevent the blast and should alone bear the cost of compensating victims. Chevron, the US oil group that part-owns the tank farm, was cleared of any liability.

Des Collins, senior partner of Collins Solicitors, who represented families whose lives were disrupted by the incident, said: "This judgment is a shocking indictment of the way in which this ultra-hazardous operation was conducted by Total.

"What is equally shocking is the degree of irresponsibility demonstrated by Total over the past three years in its failure to recognise the ultimate futility of the series of defences which it adopted from time to time.

"It is to be hoped that Total will now, even at this very late stage, provide to the residents an unqualified apology for their conduct."

A spokesman for Total said: "We greatly regret that the Buncefield incident occurred. We would stress that Total has never sought to avoid its responsibilities as a partner in the joint venture.

"We will continue to make every effort to ensure that significant process is made to settle outstanding claims and find practical ways to support the local community."

The explosion, at 6am on Sunday, December 11, 2005, measured 2.4 on the Richter scale and could be heard as far away as the Netherlands.

It happened after staff failed to notice that a tank gauge had become stuck, causing oil to overflow. The tank continued to fill past critical levels after a backup safety switch failed to trigger, causing the plant to fill with petrol vapour. Alerted by a tanker driver to the strong smell, the duty supervisor mistakenly shut off the wrong pipeline.

The blast destroyed storage operations belonging to other oil companies such as Shell and BP — both of which were claimants against Total — but also caused significant damage to properties and businesses within several miles of the plant. About 40 people were injured.

Total initially denied responsibility but later admitted that the explosion had partly been the fault of the supervisor on duty at the time and that the damage caused was foreseeable — a key point in establishing legal liability.

Instead, the focus of the trial, which began in October, shifted to whether Total alone should bear the cost of compensating the victims or whether Hertfordshire Oil Storage Limited (HOSL), the nominated operating company, and Chevron, which owns 40 per cent of HOSL, should share in the cost.

Yesterday Mr Justice David Steel ruled that all the employees working at the site had employment contracts with Total and took instructions from the oil company's head office rather than from HOSL.

In contrast, although HOSL was the nominated operator of the site, it had no employees and its board met for only two hours every six months. It could not have been responsible for day-to-day operations, the judge said.

The judge also found that Total's head office staff had contributed to the explosion by failing to put in place an adequate system for preventing the overfilling of the tanks. This was reflected in the absence of written tank-filling procedures for use in the control room after a near-accident in August 2003.

"Chevron's position that it was merely a sleeping partner in the venture has been vindicated," Ted Greeno, a partner at Herbert Smith, the leading City litigation firm that represented Chevron, said.

Chevron, which had with Total already paid out millions in compensation to victims before the case, is now likely to demand reimbursement from Total. However, Total said it will consider appealing the verdict.

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