Unison found that its members had been left with a catalogue of medical problems including headaches and back pain.

Staff who carry laptops are also worried about the risk of being assaulted, the poll discovered.

The survery of 500 careers advisers who use laptops discovered that three out of five of them complained of back or neck pains, eyestrain and headaches.

Unison now wants the Health and Safety Executive to investigate the risks associated with using laptops.

Laptops more dangerous

The union's head of local government Keith Sonnet said it was more difficult to get into a comfortable working position with laptops than with other computer equipment and because of this they probably presented a greater health risk.

He said: "Until laptops can be eliminated it is vital that employers carry out risk assessments and take steps to minimise health hazards associated with their use."