Employers have been advised to improve their procedures for tackling the growing problem of bullying in the workplace.
The Health and Safety Executive said that bullying cost businesses as much as 80 million working days a year and up to £2 billion in lost revenue.
Almost half a million people experience work-related stress at a level that they believe is making them ill, with bullying a key source of work-related stress, the organisation said.
Psychology professor Gary Cooper from Lancaster University said: "Large scale national research found that bullying doesn't just affect the people who experience it first hand, but the people who witness it too.
"It lowers morale in the office and in some cases can lead to an increase in time taken in days off work for stress-related problems. Moreover it can also impact on other areas of life including relationships and family life."
The HSE said that employers should use the time around National Bullying at Work Day on November 7th to review whether they were doing enough to secure the wellbeing of their employees.