A 1,100-tonne bridge over the Great Eastern main line into London slipped off temporary support plates, causing concrete decking to fall on to the line in front of a train, says an official report into the incident.

The accident in May this year happened near Liverpool Street station and involved a huge steel bridge, part of the East London Line project.

It had been slid into place over the early May bank holiday weekend but work was still continuing to install it in its final position.

The alarm was raised after a quick-thinking National Express East Anglia train driver spotted debris on the track ahead of him and managed to stop his train.

The incident caused massive disruption to trains and led Network Rail to ban all further work on the bridge pending an investigation.

The report by Transport for London said that low friction plates had been placed at the base of the bridge and temporary supports and left over-night. It is believed that changes in temperature led to the bridge contracting by two or three millimetres and the temporary supports being ‘ejected’.

This led to the bridge dropping about 200 millimetres, causing five pieces of concrete decking to fall on to the rail lines below.

TfL says it has now tightened up supervision of its contractors as a result of the incident. Martin Brown, TfL London Rail’s director of safety, said: “The temporary work, which involved jacking the bridge horizontally about 38 millimetres to a position over the permanent fitting, was undertaken without engineers from TfL or our main contractors being made aware of what was happening.

“The positioning of the Teflon pad was a human error, but the procedures we have should have stopped this error occurring. 

“There is a collective responsibility for ourselves and our contractors to ensure these procedures work.”

He said that contractors Balfour Beatty-Carillion had now upgraded their system of checking sub-contractors and TfL had also stepped up its overall supervisory role.

The bridge has now been bolted and welded into its permanent position without further problems.

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