Employers are losing millions of days work every year because of bullying, according to a report.

A survey of 5,300 workers, commissioned by the Trades Union Congress, says that almost half of Britain's employees have witnessed aggressive behaviour at work.

One in 10 said they had been bullied within the past six months.

Psychologists at the University of Manchester Institute of Science and Technology, who carried out the study, found that victims tended to take seven days off sick a year more than those who had not been bullied.

An estimated 18 million days' work are lost each year as a result, the study found.

Unlike schoolroom bullying, most workplace aggression is verbal or behavioural rather than violent.

But, the report says, mental bullying is just as stressful as the physical form.

Alison Campbell had worked in the marketing department of a company in Yorkshire for two years when incessant bullying from the sales and marketing manager drove her out of her job.

"She would scream and yell at us and undermine everything we did," she said.

"After two years of constant bullying I just felt I couldn't take any more. I ended up in hospital for three weeks suffering acute stress and was signed off sick for six months."

Ms Campbell said she was still feeling the psychological effects of the bullying years later.

Last month a council official in Hampshire was awarded �200,000 damages for psychiatric problems that he says were caused by his bullying boss.

Bad management style

Bullying was found to be most common in the prison service, post and telecommunications industries, teaching and the performing arts.

The report's co-author, psychology professor Cary Cooper, called on firms to develop long-term strategies for dealing with bullying.

"The findings in this study show that, with better management training and awareness, bullying is avoidable." he said.

"Workplace bullying not only damages the individual but everybody who experiences it."

TUC Secretary General John Monks called the report's findings shocking.

"These figures show bullying is rife at work and no workplace is immune," he said.

"The study suggests that bullying is often down to bad management style. That's why it is crucial that unions and employers work together to tackle what is becoming one of Britain's most worrying workplace phenomena."

However the TUC praised organisations and companies that have set up anti-bullying initiatives, including Rolls-Royce and Littlewoods.