The supermarket group faces a bill estimated at £5 million, possibly rising to £20 million, to compensate Network Rail, Chiltern Railways and passengers who use the line.

The construction work at Gerrards Cross, Buckinghamshire, was to enable a superstore to be built over the railway line. Its collapse on Thursday evening, soon after a commuter train had passed through, was celebrated with champagne by residents who oppose the Tesco development.

Engineers were at the site yesterday to try to establish what caused the collapse. They were assessing the standard of the construction work, which was running months behind schedule.

A spokesman for the Health and Safety Executive said that inspectors remained open-minded about the cause but added: “We are focusing on the way the construction work was carried out.”

Inspections and work to clear up the debris are being hampered because there is a significant risk of further collapses, with other parts of the tunnel being unstable.

The railway line, Chiltern Railways’ main link between London Marylebone and Birmingham, was at the bottom of a deep cutting.

More than 300 steel-reinforced concrete arches were erected to create a tunnel about 320 yards long, with a flat surface to support the store and car park.

Rubble and ash used to fill in the cutting blocked the line yesterday and Network Rail, which owns the track, said that it would take “several weeks” to clear.

Commuters were warned, however, that there could be further delays if the remaining sections of the tunnel need to be demolished or if the cuttings have been destabilised.

Chiltern Railways has continued long-distance train services by using an alternative route, though it adds up to 40 minutes to the trip between London and Birmingham.

Replacement buses have been laid on between Beaconsfield and Amersham, between High Wycombe and Maidenhead, and between Denham and West Ruislip.

More than 50 yards of the concrete tunnel collapsed 80 yards from the south entrance and a Network Rail spokesman said that a “full engineering assessment” would take at least until tomorrow to complete. Only then could work to clear the line begin.

The collapse was witnessed by the driver of a train at Gerrards Cross station. He alerted controllers who halted all nearby services.

Many residents of Gerrards Cross oppose the development, which was given approval by John Prescott, the Deputy Prime Minister, after a planning inquiry.

Gail Clarke, of Gerrards Cross, said: “When I heard that no one was hurt in the collapse I did a merry jig. Tesco’s reputation will be in tatters after this fiasco, and they deserve all the flak they get.”

Peter Hardy, leader of South Bucks District Council, called for an independent inquiry into the designs and construction techniques. “We must be grateful that there was no loss of life or injury, but that is no thanks to Tesco or to the contractor,” he said.

The contractor, Jackson Civil Engineering, of Ipswich, denied suggestions that standards had been compromised by demands to finish the job quickly.

Tesco said that it would address issues of cost and blame in the future. A spokesman said: “For now, our priority is to get the rail line reopened.”

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