A number of services have been cancelled Train company criticised

The slippage was reported on Thursday near the Chipping Sodbury tunnel, and had closed a main line between Swindon and Bristol Parkway stations.

The train operator said it hoped to run a full morning peak service between south Wales and London on Friday.

But journeys will be up to 30 minutes longer due to temporary signalling.

Off peak, only an hourly service will run in both directions between London Paddington and Swansea, with extended journey times of 30 minutes.

'Completely rebuilt'

First Great Western spokesman Richard Smith, said the line needed to be "completely rebuilt", including stabilisation work, new foundations, and new track and signalling.

"Until we can get engineers to the site to see the damage, we won't know what caused it, but it has covered several boxes that control points," he said.

A Network Rail spokeswoman added: "We've got engineers down there inspecting the site and looking to restore services as soon as we can."

She attributed the main problem to the bad floods the region had experienced recently.

"Poor conditions meant the bank was saturated and affected the area's signalling boxes."