Four workmen who were flung 80ft to their death from a motorway bridge were working in a gantry with insufficient brakes while risks to safety were repeatedly ignored, a court heard today.

Yarm Road Ltd, formerly known as Kvaerner Cleveland Bridge Ltd, and Costain Ltd, are being sentenced in a hearing likely to last two days, after pleading guilty to breaches of health and safety law at a previous hearing at Bristol Crown Court.

Paul Stewart, 24, of Newcastle upon Tyne; Ronnie Hill, 39, of Glasgow; Jeff Williams, 42, of Newport, Gwent; and Andy Rodgers, 40, of Middlesbrough, died when they fell from a gantry while working on strengthening the Avonmouth Bridge, which carries the M5 near Bristol, on September 8 1999.

Mr Philip Mott QC told the court there had been "persistent and blatant breaches" of the law over a long period of time, with safety advice from technical advisors, given only a week before the accident, not acted upon.

He said that if the companies had undertaken a major review of safety procedures, rather than simply a "superficial response, it might just have been in time to save the men killed in the accident".

The court heard that the companies involved were both major firms, neither struggling nor underfunded, who had won the contract for the six-year work worth £150 million to widen and strengthen the bridge.

But Mr Mott said that the two firms had been breaching health and safety law over a long period of time, exposing their workmen to danger, as well as people travelling by road or rail under the bridge, and those who lived or worked under the bridge.

He said: "The seriousness lies not in the number of breaches but the very considerable gap between the level of managerial and technical control which should have been in place and that which was actually taking place over a substantial time.

"This was not a single fault on a single day."

The court heard that there had not been sufficient risk assessment carried out, with equipment left untested.

Mr Mott said human error and structural or technical problems had not been foreseen and the risks involved eliminated, according to Health and Safety guidelines.

In addition, workmen and supervisors had not been given sufficient training, with an audit only a week before the accident by a separate company showing that workers were not using the turfers properly.

He said that there had been warnings, where gantries had moved in an uncontrolled fashion up the slope because of the wind on previous occasions, but that no action had been taken.

A judge can impose unlimited fines for the breaches of the Health and Safety at Work Act 1974, as well as costs which total £525,000.

Yarm Road Ltd, of Hammersmith, west London, was charged with two offences under the act, failing to ensure that persons not in its employment were not exposed to risks, and also failing to ensure the safety of its employees, including Mr Williams, Mr Stewart and Mr Rodgers, both of which it has admitted.

Costain Ltd, of Maidenhead, Berkshire, was charged with one count under the act, failing to ensure that persons not in its employment, including Mr Williams, Mr Rodgers, Mr Stewart and Mr Hill were not exposed to risks, which it also admitted.