Sick leave is costing the UK economy around �13bn a year, with back pain and stress being the major cause of time off, according to new research.

The Chartered Institute of Personnel and Development says sickness costs businesses an annual average of �520 for each employee.

While the nation's health is not deteriorating, the survey found that UK workers were taking more sick leave, clocking up an average 10 days a year.

The institute questioned more than 1,300 organisations about why employees went sick and how much it cost businesses.

Costly leave

Stress was found to be the leading cause of long-term illness among white collar staff.

Manual workers were more likely to cite back pain as the number one reason for sick leave lasting more than four weeks.

The findings are higher than those in a survey carried out by the Confederation of British Industry (CBI).

The CBI research estimated that the cost to UK firms was around �12bn in 2001, up �1bn on the previous year.

The survey also calculated that UK workers took an average of seven days off a year.