Collapse of a rafter to support retractable roof results in loss of day's work for 3000 operatives

Contractors working on Wembley stadium are set to claim at least £600,000 after the collapse of a beam in the stadium's roof forced contractor Multiplex to evacuate the site.

About 3000 workers from the site were sent home after the incident on Monday, when a 50-tonne steel rafter fell half a metre from the stadium's roof. The incident, which came a month after the Football Association announced that the stadium would not host this year's FA Cup final, is the latest in a series of setbacks for the project.

The workers, who were evacuated from the project at 8.45am, were sent home on full pay at an estimated total cost of £600,000. Project sources have suggested that contractors are likely to seek to recover the sum plus damages for any additional delays.

A senior source at union Amicus, which represents the electricians and steelworkers on Wembley, said: "Some contractors will definitely try to claim the money back. For us, it is just a relief that the fault was not in the permanent weld, as then the works would have had to be shut down for far longer."

A detailed forensic investigation by Multiplex and steel contractor Hollandia, which was working on the section when the incident occurred, has yet to determine its cause.

Martin Tidd, Multiplex's managing director, said an investigation by structural engineers had found that the problem with the rafter, which runs from north to south across the stadium and partially supports the retractable roof, was not found on other beams in the stadium.

The slippage happened when workers were preparing the beam for welding into its permanent position.

Tidd said he could not comment on whether the incident would cause further delays to the project, which is four months behind its original schedule. He said: "We are currently investigating the incident. When our investigation is complete we will be able to ascertain whether there is any long-term affect on the programme."

Workers on the stadium on Monday reported hearing a "huge bang" as the rafter fell. One site source who was working close to the beam said: "People were yelling ‘The roof's going, the roof's going!' I've never seen people run like that."

The Health and Safety Executive is investigating the incident, and was due to visit the site on Wednesday as Building went to press.