The warning comes after the case of British woman Catherine Sanderson in France, who has recently won her case for unfair dismissal against her British employers who sacked her for writing a blog.

She had been writing a blog using the name "petit anglaise".

In her blog she had written about her work and personal life without revealing any identities.

However, there were two photographs of her on the site which her former employers, the accountancy firm Dixon Wilson, claimed identified her and therefore themselves as her employers.

Dixon Wilson claimed that they had sacked her as she had wasted time at work on her blog, and her comments could have bought them into disrepute.

The firm were ordered to pay 44,000 euros, plus costs.

Hegarty's employment partner Tim Thompson said: "This is a real test case regarding the use of blogs and has wide implications for employers throughout Europe.

"Employers should ensure they have a policy in place about blogging but must also tell their staff about the existence of the policy.

"It is now common for firms to have e-mail and internet policies. But they need to be extended to include blogging.

"If the employee has made comments in a blog which could damage the company or reveals confidential information then it might be treated as misconduct.

"I've advised clients who caught an employee updating a blog at work earlier this year.

"The employee was disciplined and told that if they continued to write the blog at work they may be later dismissed."