Yet when an Indian court convicted seven former employees of Union Carbide for negligence yesterday — more than 25 years after the 1984 accident — the sentences given were no harsher than those for causing a fatal car accident. It seems unlikely that they will serve any time in jail.

The court in Bhopal sentenced the seven former managers of Union Carbide’s Indian subsidiary — the company is American owned — to two years in jail, fined them 100,000 rupees (£1,465) each and allowed them to remain free on bail pending appeal. It also convicted Union Carbide India, the subsidiary, but ordered it to pay only 500,000 rupees in compensation.

Victims of the disaster and the activists who help them were outraged, describing the sentences as “too little, too late” to compensate for the suffering caused or to prevent similar accidents in the future.

Hundreds of protesters gathered outside the courthouse, shouting slogans and waving placards saying “Hang the guilty!”. “This verdict sets a very sad precedent,” said Satyanath Sarangi, president of the Bhopal Group for Information and Action. “In fact, it will encourage hazardous corporations to kill more people and maim them because they can do it so easily because a disaster like Bhopal can be converted into something like a traffic accident.”

The verdict throws a fresh spotlight on the issue of corporate responsibility for industrial accidents just as a legal battle looms over the cost of cleaning up the huge oil spill from a BP rig in the Gulf of Mexico.

It could also influence a debate in the Indian Parliament over the extent to which foreign companies that enter India’s lucrative civilian nuclear market should be liable for accidents.

The Indian Government said that about 3,500 people died in the three days after the Union Carbide plant accidentally released 40 tons of deadly methyl isocyanate gas into the air in the early hours of December 3, 1984. It estimates that the lingering effects raised the death toll to about 15,000 over the next few years.

But activists say the leak killed at least 25,000 and affected the health of up to 500,000. India originally tried to sue Union Carbide for $3.3 billion in damages in the United States, but agreed to accept $470 million in compensation in an out-of-court settlement in 1989.

Union Carbide was then bought in 2001 by Dow Chemical Co, another American company, which said that the legal case had been resolved, and responsibility for the site now lay with the local government.

However, India’s Central Bureau of Investigation continued with its case against Warren Anderson, the American head of Union Carbide at the time of the leak, as well as eight managers of the Indian subsidiary.

Mr Anderson, now 89, was arrested in India after the accident but was released on bail and allowed to leave the country. He has resisted all Indian attempts to have him extradited.

One of the Indian managers has since died, so yesterday’s verdict applied only to the seven surviving ones, all of whom are in their 70s or 80s.

They included Keshub Mahindra, 86, the multimillionaire chairman of the tractor and truck manufacturer Mahindra & Mahindra, who was chairman of Union Carbide India at the time of the accident.

Human rights activists said that the seven were unlikely to serve any time in prison as their appeals would take several years to be heard by India’s massively overloaded courts.

“These are historic convictions but it is too little, too late,” said Audrey Gaughran, director of global issues at Amnesty International.