A bolt of electricity from overhead powerlines started a fire in the Channel Tunnel, leading to nearly a week of transport disruption for Kent.

Operation Stack brought the county to a standstill in January after the blaze in the tunnel closed the freight transport route used by hundreds of lorries every day.

The Rail Accident Investigation Branch will work with French authorities to examine the cause of the fire.

An initial investigation, published today, has found the blaze probably started when electricity arced between overhead powerlines and a train as it entered the tunnel on the UK side, setting light to a lorry.

The arc caused the power to shut off, stopping the train, but the tunnel's control centre gave the driver permission to continue when the electricity came back on 26 seconds later.

The truck continued to burn as the train made its way towards France, only setting off a fire alarm 29km into the tunnel, still 21km from the exit.

An alarm also sounded on the train and power went off for the second time.

All 38 passengers and three staff were travelling in one coach immediately behind the locomotive, and the driver brought the train to a "controlled stop" next to a service passage, about 16km from the French exit.

It took seven minutes for the train to be evacuated, and firefighters moved in to tackle the flames.

The blaze took nearly three hours to bring under control, with many more spent dousing the red hot metal to cool it down.

The fire destroyed two lorries and caused damage to coaches and the tunnel lining.

Eurotunnel has said it is reviewing procedures for arcing events near the tunnel entrance, with the intention of reducing the consequences of any resulting fire.

The company is also considering other control measures to reduce the chance of a similar accident.

Investigators have not reveled when their detailed findings will be published.

Operation Stack was brought in to manage the congestion caused by the fire.

Lasting four days, the latest installment of stack saw lorries stretching back 20 miles at its peak, prompting various agencies to explore a better solution to Kent's transport problems.

Kent County Council has floated plans for a 3,000-space lorry park on land at Westenhanger in Folkestone.