Small business owners should re-examine their sickness procedures and introduce back-to-work interviews to cut down on cases of bogus sickness, according to an employment law company.

Research by Peninsula claims that the total cost of sickness absence to companies is almost £21bn a year, with £3.5bn of that down to false cases. The survey claimed that 17% of all absence is bogus.

It also indicated that the average number of days taken off sick by an employee is 16, double the figure from 2002. A total of 480m days are lost due to absenteeism, it added, with 81.6m of these due to people taking time off sick when they are not actually ill.

The most common complaint for someone phoning in sick is flu or its side effects, the survey revealed.

Peninsula is advising companies to pay more attention to trends in sickness, for example staff taking a lot of Mondays or Fridays off or days when major sporting events are held, and enforce back-to-work interviews when staff return from a stint of sickness.

"It is all too easy for a worker to ring in sick. They still get paid for it and there is no follow up regarding the excuse as to why the employee was off," says Mike Huss, employment law director at Peninsula. "Return-to-work interviews should be enforced to give the employer and the employee the chance to sit down and discuss why they were absent from work.

"This can dissuade employees from calling in sick, when bogus, as a sense of guilt may hold them back," he added. "The employer must make it known that bogus sickness will not be dealt with lightly."

Peninsula has recently invested £755,000 in its Business Wise computer tool designed to help employers identify fraudulent absenteeism patterns.