INVESTIGATIONS are under way to find out what caused a major gas leak which resulted in hundreds of people being evacuated from their homes.

Transco engineers are studying sections of pipes, and samples have been sent to experts for analysis.

But a spokesman for the firm said: "It could be months before we get an answer from the pipe analysis - it's quite an involved process."

Suspicions are that last week's cold snap - combined with the fact that Bolton Road carries a lot of traffic, including heavy goods vehicles may have caused the damage.

Engineers worked through the night to repair pipes after firefighters cordoned off a 200-square-metre area around Bolton Road, Westhoughton, last Thursday. Residents were not allowed to return to their homes until Sunday.

Engineers discovered cracks in the 18-inch main which runs down the middle of the road, and were forced to dig down to repair the pipe.

A spokesman for Transco said this kind of leak had not happened in the area before, and was rare.

He added: "Our priority was safety. We had people constantly asking if they could get back into their houses, but it was just too dangerous."

Transco will now start counting the cost of the damage, as claims for expenses such as taxis and clothing start to come in from the residents who had to be re-housed.

"We had two operations on the go - the repairs, and looking after people who had been evacuated," the spokesman said.

"We organised medication for people who needed it and social services accommodation for an elderly lady with special needs."

Westhoughton High School was closed on Friday, with 1,200 pupils missing lessons. The Town Hall was also closed.

The alert began at 10pm on Thursday, when a passer-by smelled gas on Bolton Road and witnesses reported seeing the asphalt "bubbling."