A report into the incident, which occurred on 28 May and caused five pieces of concrete decking to fall onto rail lines below, has been released.

It has found that the bridge dropped 200mm after sub-contractors, using temporary supports, made final adjustments before placing it on its permanent fixtures.

A Teflon plate was wrongly positioned between the base of the bridge and the temporary supports.

It is believed that as the bridge cooled down in the evening this resulted in it contracting two or three millimetres. This led to a movement, which caused the temporary supports to be ejected from their position, resulting in the east end of the bridge dropping onto its permanent fixtures.

The report also found that their working methods were not cleared with either the site principal contractor - a Balfour Beatty/Carillion joint venture - or TfL project engineers.

The incident caused services into Liverpool Street station to be suspended overnight.

TfL has tightened up supervision over its contractors as a result of the incident and will make its findings available to the industry to prevent the incident from being repeated elsewhere.