Prosecutions of companies found responsible for deaths – from rail crashes to accidents at work – are expected to rise significantly under laws that took effect yesterday.

Companies that might otherwise have been able to avoid prosecution or conviction will, under the Corporate Manslaughter Act, be more easily brought to justice and will face the prospect of heavy fines. In 2006-07 alone 241 people were injured fatally at work, according to the Crown Prosecution Service. Since 1992 there have been 34 prosecutions and six convictions.

Under the old laws a company could be convicted only if the “directing mind” or senior individual could be identified as responsible for gross failings leading to a death. The new Act enables the collective actions of a company’s management to be examined. Although individuals cannot be jailed, companies face unlimited fines.

The measure, which comes into force after decades of lobbying by campaigning groups, trade unions, relatives“ and others, follows a series of disasters where prosecutions collaped or could not be mounted. They included the deaths of 187 people after the capsizing of the Herald of Free Enterprise in 1987; the King’s Cross Underground fire in the same year (31 deaths); the Piper Alpha oil platform disaster in 1988 (167 deaths); and the Paddington rail crash in 1999 (31 deaths).

Adrian Bever, a partner with the corporate law firm Addleshaw Goddard, said that the measure was the “most significant change in health and safety law for 30 years”. Guy Bastable, a partner at the London solicitor BCL Burton Copeland, said although penalties were only fines, the consequences could be crippling.

The Sentencing Advisory Panel had suggested fines of up to 10 per cent of a company’s annual turnover during the previous three years, he said. “For the largest organisations such a fine could easily be hundreds of millions of pounds.” The Act would also apply to other organisations such as some government departments, police forces, partnerships and trade unions, he said.

Kevin Elliott, regulatory partner at the law firm Eversheds, gave warning that linking fines to turnover would put small firms out of business. “While we agree that fines for significant health and safety breaches should be high enough to reflect the offence, surely the point is not seriously to jeopardise the economic viability of many businesses which are ostensibly very well run, including in the area of health and safety management,” he said. Swingeing fines would also hit the capital pot available for future safety investment.

Insurers said that the Act was a warning to businesses to ensure proper healthy and safety measures. Tom Sheffield, technnical director at Aon, the risk adviser and insurance broker, said: “This serves as a wake-up call to businesses to update their health and safety controls for the wellbeing of their employees and the public.”

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