The study - based on a survey of 3,500 UK companies - concluded that businesses need to take firm action on the use of social networks at work. Some firms have already banned employees from accessing Facebook.

Mike Huss, director of employment law at Peninsula called on all firms to block access to sites such as Facebook. He asked: "Why should employers allow their workers to waste two hours a day on Facebook when they are being paid to do a job?" He said that loss of productivity was proving a "major headache" for firms.

"The figures that we have calculated are minimums and it's a problem that I foresee will escalate," he said.

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