The cost to businesses of UK workers shopping online for Christmas when they should be working will reach £260m a week over the next few months, according to web filtering firm Bloxx.

Assuming an average of just one hour spent shopping online during the working week, and using an average hourly wage of £12.50, Bloxx estimates that UK employers could lose £260m a week in lost productivity.

Bloxx said that the figure is backed up by the Business Software Alliance, which claimed that 46 per cent of online shopping happens during working hours.

"With the Christmas shopping frenzy now starting in earnest and remaining throughout the rest of the year, the cost to UK businesses due to staff spending inordinate amounts of time shopping online during working hours could be huge," said a statement from Bloxx.

Paul Irvine, sales and marketing director at Bloxx, added that it is not in the nature of most companies to stop their employees doing Christmas shopping at work.

"However, with the addictive nature of online shopping, it can be all too easy for employees to get carried away and end up spending hours online during the working day," he said.

Kirsty Ayre, a partner at law firm Pinsent Masons, warned that it is important for companies to set a clear acceptable use policy for internet use during working hours.

"Employees need to know what is acceptable and what the consequences could be for breaking the policy," she said.

According to UK figures, online sales reached £10.9bn last year, growing 13 times faster than the overall retail sector.