On the face of it, a council using fake Facebook profiles to gather information about people through the social media might seem alarming.

To some, the idea of town hall officers snooping on internet users is a worrying step in the onward march of state power.

That is the way this week's story regarding two councils in North Wales looks to the campaigning group Big Brother Watch.

Commenting on the use of 'pseudonym' Facebook profiles to gather information on the sale of counterfeit goods they told LocalGov: 'It is shocking that local authorities are intruding in these spaces by pretending to be someone else and even training staff in such covert measures.'

There are clearly important issues involved when anyone - including employees of public bodies especially, perhaps - pretends to be someone else in order to gather information.

In some circumstances it is unacceptable. Using covert methods is usually only justified if the investigation is clearly in the public interest and there are no other means of gathering the information required.

Tracking down criminals selling potentially dangerous goods to the public clearly falls well within that definition.

The Chartered Institute of Trading Standards points out that using fake Facebook profiles is similar to through the 'test purchasing of under-age goods' method of snaring shopkeepers illegally selling cigarettes or alcohol to young people.

Few would argue that sending a fourteen-year-old into a shop to buy cigarettes to see if the shopkeeper is breaking the law, in a properly conducted investigation, constitutes an attack on civil liberties.

There are clear guidelines under the Regulation of Investigatory Powers Act for authorities using covert profiles to gather intelligence, the CITS points out.

Trained officers are overseen by a national body, it says, evidence is logged and covert investigations are conducted in the interest of public safety, often aimed at stopping dangerous and illegal counterfeit products from reaching consumers.

Local authorities, like other public bodies, have to be keenly aware of their rights and responsibilities under the law.

They argue, rightly, that in the case of counterfeit goods, the need to protect the public fully justifies the use of fake profiles on Facebook.

It just so happens that Facebook are currently regarded with suspicion for all sorts of reasons from their tax affairs to the way they control material published online.

But that is not relevant to whether it is a source of potentially valuable information in the fight against crime.

Adopting a fake persona to track down illegal activities in a properly controlled and regulated way is a very different kind of activity to gratuitous snooping on people merely to find out more about them.

Unfortunately Big Brother Watch does not appear to understand the difference.