One of the five companies prosecuted in connection with the Buncefield oil depot explosion has admitted it breached health and safety laws.

Watford-based Total UK today pleaded guilty to two charges under the Health and Safety Act and one under the Water Resources Act, at the start a highly anticipated trial.

Four other companies, TAV Engineering Ltd, British Pipeline Agency Ltd, Motherwell Control Systems 2003 Ltd, and Hertfordshire Oil Storage Ltd (also based in Watford), all deny responsibility.

The explosion, on December 11, 2005, was the biggest ever recorded in peacetime Europe, and caused an estimated £1 billion of damage. It also forced the evacuation of more than 2,000 people form their homes in the Hemel Hempstead area.

Miraculously, nobody was killed.

Total UK and Hertfordshire Oil Storage Ltd were both charged with failing to ensure the safety of their workers, as well as allowing fuel and chemicals to pollute groundwater.

Total, however, is not expected to be sentenced until the conclusion of a trial against the defendants – to start at St Albans Crown Court on April 14 – has been concluded.

Total UK said in a statement: "As criminal proceedings continue against a number of other defendants, it would be inappropriate to comment further, other than to say that Total UK regrets the unfortunate events at Buncefield in December 2005 and would like to apologise to all those affected by the incident."