If Britain's workplaces appear to be bereft of employees this morning, there is a reason - it is the most popular day of the year for throwing a "sickie".

The average employee takes nine days' fake sick leave a year, according to a new survey, and Mondays and the first week of February are favoured for having an extra day off.

"The first bank holiday seems a long way off, the days are gloomy and many people are still feeling the post-Christmas blues," said Cary Cooper, a professor of organisational psychology and health at Lancaster University.

The poll of more than 4,000 people for the Sky Travel channel found that almost half of the British workforce called work and pretended to be sick at least once a year, which cost an estimated £4bn in lost business.

Only 5 per cent of people said they had been caught out by their bosses, but computer software has now been developed that allows employers to spot suspicious sick-leave patterns.

Britons may be partial to taking a sickie this month, but a survey by the Trade Union Congress last week found that more than five million people put in unpaid overtime that amounted to an extra day a week of work.