Call-centre workers are suffering from a new industrial disease: repetitive voice injury. According to the Royal College of Speech and Language Therapists, increasing numbers of call-centre workers are being referred to speech therapists because they are losing their voices.

Long hours and little opportunity for even a drink of water are behind the "disease". "It's a growing problem," said Paul Carding, a professor of voice pathology and national adviser to the college. "There is increasing evidence of people taking time off because if they can't use their voice they can't work. At its most severe these people can't hold down a job. They have pushed their voice to the absolute limit. In some cases, voices really struggle to recover."

Teachers remain the most common professional group to require speech therapy, but call-centre workers have now become the fastest growing "at risk" sector.

Nearly 800,000 people work in the call-centre industry in the UK, even though many high-profile companies have outsourced their call centres to India, including HSBC. National Rail Enquiries outsourced half its calls to India earlier this year.

But the call-centre industry denies that "call centre-itis" is a real problem. Ann-Marie Forsyth, director of the Call Centre Association, said: "This is not an issue specific to call centres. But we encourage members to be aware of all the risks surrounding the occupation, and organisations need to make sure that water is available throughout the day."