A quick-thinking train driver averted a “major disaster” on the Ipswich to London mainline by slamming on the brakes to avoid debris on the tracks that had fallen from a bridge.

A quick-thinking train driver averted a “major disaster” on the Ipswich to London mainline by slamming on the brakes to avoid debris on the tracks that had fallen from a bridge.

Passengers on the National Express East Anglia train were seconds from disaster when he managed to bring the service to a controlled stop just outside Liverpool Street station, it emerged last night.

Thousands of commuters faced heavy delays following the incident on Wednesday evening and the station was closed during yesterday's morning rush hour.

Industry sources were asking questions about why fast-running trains were still being allowed to use the track while delicate engineering work was being carried out on the 800-tonne bridge near the station.

Keith Norman, leader of train drivers' union Aslef, said: “This could so easily have been a major disaster. The driver did well to bring his train to an immediate controlled stop - we wholeheartedly back the calls for a full inquiry into exactly what happened - and the results must be made public for the benefits of passengers and rail staff.”

A National Express spokesman praised the unnamed driver saying: “Clearly he acted extremely quickly and carried out all the correct procedures.”

The affected bridge - GE19 - was being worked on by engineering companies Balfour Beatty and Carillion on behalf of Transport for London (TfL).

Network Rail said that its chief executive has written to TfL's commissioner Peter Hendy to seek urgent answers.

A spokesman said: “Because of concerns over TfL's handling and management of both the project and its contractors, Network Rail has banned work on the bridge, effective immediately. This will remain in place until TfL has completed an investigation and reported back on the causes of the incident and what measures it will be putting in place to prevent a repetition.”

Network Rail's director of operations and customer service, Robin Gisby, said: “Passengers rightly want an explanation, as do I. Passengers deserve an apology for the disruption they suffered last night and this morning and I want assurances that such an incident can't and won't happen again.”

Part of the new East London line which will open in 2010, the bridge was constructed about a month ago. Workmen were using jacks to inch it into its final position when one failed and the bridge moved, causing debris to fall onto the fast mainline tracks below.

The incident happened when the driver of the 7.15pm Liverpool Street to Southend Victoria service saw the tracks blocked. He slammed on the breaks and prevented any damage despite sliding into the debris. There were no injuries.

Network Rail was forced to turn off the overhead 25,000-volt power lines, leaving three trains stopped on the lines. Police and rail staff led the passengers to safety - walking them back to Liverpool Street and Bethnal Green stations.

The new bridge already had a jinxed history.

Work to demolish the previous bridge overran after Christmas, causing huge disruption to commuters returning to work in the New Year. Network Rail was fined a total of £14.4 million and heavily criticised in an inquiry,

A TfL spokesman said: “We would like to apologise for the inconvenience caused. We will be working with other contractors and the rail authorities to carry out a full investigation. We will need to look at completing the work at a later date.”

Services started running in and out of Liverpool Street by about 9.30am yesterday with normal services resuming later.

Asked whether National Express would attempt to recoup any losses arising from the incident, a company spokeswoman said: “There is a standard industry assessment of any serious disruptive incident, such as the one that happened on Wednesday night. Costs would be allocated within those agreed procedures within the industry.”

She said that compensation was offered to customers delayed by half an hour or more as a standard practice.

People should ask at their local station for a leaflet or contact the National Express customer services centre on 0845 600 7245.