Nightshift cancer probed.
It came as the Danish government began paying out to women who have developed breast cancer after long spells working nights.
The Government's Health and Safety Executive will look at evidence that missing sleep and long-term tiredness is linked to a series of diseases.
A report by the UN's World Health Organisation claimed women working late for more than 30 years had a greater risk of breast cancer than those who did not.
Health and Safety Executive chief Dr John Osmond said they had ordered an inquiry over the claims.
Occupational health expert Professor Andrew Watterson, of Stirling University, said: "There is a big public health problem here.
"The evidence has been good over a long period about cardiovascular disease and night work, gastro-intestinal problems and nights."