A huge rise in the number of claims for stress-related pressures at work is causing alarm among insurers.

They are calling on the UK's employers to start treating staff more fairly, by cutting back on long hours and stop bosses bullying workers.

One of the UK's largest income protection insurers, Unum, says its claims for stress have risen by 88% over the last seven years, while those for chronic fatigue syndrome are up by 40%.

Unum was responding to a recent survey from BMRB International among 1,200 full and part time workers which found two thirds of them were stressed, with some 73% admitting it was affecting their performance.

Eugene McCormack, Unum's marketing director said: "This survey should be seen as a wake up call for the UK's business community. They appear to be allowing the working environment to become increasingly stressful and it cost could them."

Unum is campaigning for employers to move away from long working days, which it says do not result in increased efficiency, only increased levels of illness.

Other income protection insurers such as Royal & SunAlliance and Norwich Union also say they have been hit by increased levels of claims for stress.

The annual cost of stress-related sickness to British business is now more than £4billion, according to Professor Cary Cooper, Bupa professor of organisational psychology and health at University of Manchester Institute of Science and Technology (Umist).

Professor Cooper warns that stress levels in Britain are higher than in any other country in Europe and that they will increase rapidly in the next decade.

Although some private medical insurance policies will pay for psychiatric treatment for stress problems, those off work for long periods need to have been covered by income protection. This type of insurance pays for the amount of time someone is off work and typically offers a tax-free monthly benefit of around 60% of salary.

But, only around 11% of the UK population is covered by income protection. It is expensive if bought on an individual basis and while some companies provide it, many people in high pressure jobs have no insurance at all.

Critical illness insurance, which is more popular than income protection, does not cover stress. Instead this pays out on diagnosis of a number of severe conditions such as heart attack, stroke or cancer.

Yet the most likely reasons for long term absence from work are stress and back problems.

Many people though are just not able to afford both income protection and critical illness cover - someone in their 30s, for example, could be paying over £80 a month in premiums. This means they effectively have to take a gamble and predict what is likely to be the best type of cover for them.