Working long hours or overtime massively increases the risk of job-related illnesses and injuries, research has found. Those who work overtime are 61 per cent more likely to suffer occupational injuries than those who do only their contracted hours.

Working at least 12 hours a day is linked to a 38 per increased risk of injury, and a minimum 60-hour week is associated with a 23 per cent greater chance of being hurt at work. Injuries were particularly likely towards the end of long shifts, as workers became tired and stressed, the researchers found.

Campaigners said the study showed the need for the Government fully to implement the European working time directive, which would limit workers to a 48-hour week. Ministers have insisted on preserving Britain's right to opt out of the directive, despite criticism that employees are being forced into long and potentially unsafe working hours.

The findings from the study are published today in the journal Occupational and Environmental Medicine. American researchers studied the job records of almost 90,000 people in different industries between 1987 and 2000. They focused on job-related injury and illness rates including musculo-skeletal problems such as back pain, cuts and bruises, fractures and other occupational diseases such as skin complaints or respiratory conditions.

Even when the statistics were adjusted to factor out the increased hazards of certain jobs compared to others, the risk associated with longer hours and overtime remained.

Research showed the crucial cut off point came when employees had been working for more than eight hours a day. For every additional two-hour block worked after that, there was an extra injury per 100 hours worked.

The lead researcher, Professor Allard Dembe, from the University of Massachusetts Medical School, said: "The results suggest special attention needs to be paid to establishing protective measures for people working overtime. Other approaches might include periodic rest breaks and employing more people to work fewer hours."

More than a third of people now work between 40 and 50 hours a week and one in 10 works 50 to 60 hours. The average Briton works 37.1 hours a week, the same as Germany but two hours longer than the French . Stress is now the number one cause of absenteeism in the workplace and costs £3.7bn a year in lost productivity and health care.