The court has overturned a decision by the Avon county coroner to refuse to hold an inquest into the deaths of four men. An inquest will now be held.
If the inquest returns a verdict of unlawful killing the case will be referred to the Crown Prosecution Service. The CPS could then charge the contractors with corporate manslaughter.
The court conducted a judicial review of the coroner's decision to refuse to hold an inquest after an application by George Stewart, the father of one of the victims. The coroner declined to hold an inquest last December because the Health and Safety Executive had completed successful prosecutions.
David Bergman, director of the Centre for Corporate Accountability, said that because the contractors had pleaded guilty their behaviour had not been scrutinised.
"Serious breaches of health and safety law occurred on the site, and an inquest would give the bereaved an opportunity to find out exactly what caused the accident," he said.
Contractors Yarm Road, formerly known as Kvaerner Cleveland Bridge, and Costain admitted breaches of health and safety regulations. Each firm was fined £500,000 and ordered to pay £525,000 in legal costs.
An inquest would allow the bereaved to find out what happened
David Bergman, director, Centre for Corporate Accountability
Four men died in the accident in the course of work to strengthen the Avonmouth Bridge over the M5 near Bristol.
Paul Stewart, 23, Ronald Hill, 38, Andrew Rogers, 40, and Jeff Williams, 42, fell more than 80 ft when the gantry they were standing on collapsed. The High Court heard that the contractors had allowed persistent and blatant breaches of health and safety law during the work on the bridge.
The judge in the original prosecution said the accident could have been prevented by "a number of simple measures".
One man died and two others were seriously injured when a concrete staircase collapsed at a new-build project in Ringsend, Dublin.