INVESTIGATORS are looking into the cause of a series of explosions on commuter trains operated by South West Trains.

The Rail Accident Investigation Branch (RAIB) said there was a blast in under-floor equipment of a South West Trains service as it left Guildford, Surrey, earlier this month.

Debris, including fragments described as "quite sizeable", were found in the car park and on to platforms as the 14.37 service left the station for London Waterloo on July 7.

No injuries were reported.

The RAIB said similar - but smaller - explosions had occurred on at least two previous occasions and were caused by a build-up of gas caused by a manufacturing defect.

It added: "Industry parties were in the process of devising possible solutions to the problem at the time of the 7 July accident and are continuing to do so."