Paul Bennett, head of Bennett’s Legal in Shrewsbury, said while the numbers were relatively small – jumping from five cases in 2009 to 20 in 2010 – it highlighted a worrying trend.

He said: “Social networking, in particular the use of Facebook and Twitter, has become part and parcel of everyday life but it is causing huge problems in the workplace.

“We have dealt with a number of cases where there have been dismissals or serious disciplinary hearings over employees’ use of sites like these. Some have centred on an employee’s excessive and unprecedented use during work hours, while others have involved libelous or defamatory statements made about fellow staff members.”

Mr Bennett urged businesses to draft a clear policy on the use of social networking sites and deal with it within a contract of employment.

He explained: “Businesses need to set out a clear policy from the outset when it comes to social networking so at least the employees know where they stand.

“You should also be careful when it comes to outsourcing the control of your online reputation and ensure you have sufficient say in who – and how – it is operated. If not, you can leave yourself at the mercy of the punitive libel and defamation laws.

“It is a total myth that putting ‘the views expressed here are my own and not of the company I am employed by’ protects you. It doesn’t, as both the individual and the company can still be sued.”