A council that used controversial powers to spy on a family to check whether they were living in the correct school catchment area has done the same to keep an eye on local fishermen, it emerged yesterday.

Poole borough council is using the Regulation of Investigatory Powers Act (Ripa) - a law brought in to combat terrorism and cyber crime - to scrutinise people gathering shellfish.

The Dorset harbour has valuable populations of cockles, oysters, mussels and clams. Officials used the controversial law to make sure stocks were not being harmed or taken from banned areas.

Human rights campaigners said the revelations, which the council released under the Freedom of Information Act, illustrated why the Ripa law should be reformed.

Shami Chakrabarti, director of Liberty, said: "You do not use a sledgehammer to crack a nut. You can care about serious crime and terrorism without throwing away our personal privacy.

"The law must be reformed to require 'sign-off' by judges, not self-authorisation by over-zealous bureaucrats."

Last month the council admitted spying on a family to check they were living in the correct school catchment area. Jenny Paton, 39, Tim Joyce, 37, and their three daughters had their movements scrutinised and timed by an undercover official.

A detailed log of the family's activities was kept with statements including "curtains open and all lights on in premises", but no action was taken against them.

Since then it has emerged that councils are using the powers for a variety of offences, such as littering or dogs fouling pavements.

Some local authorities have used the act more than 100 times in the last 12 months to conduct surveillance, mainly against people suspected of being linked to rogue trading, benefit fraud and antisocial behaviour involving criminal damage.

Poole and other councils have argued that the act is not simply intended to target very serious criminals and terrorists.

According to the Home Office, the act "legislates for using methods of surveillance and information gathering to help the prevention of crime, including terrorism".

Poole said it had used the act 17 times since 2005. In March of that year, it used the law to "ascertain which person caused damage to a barrier". In September 2006, Poole used it again to "identify persons continually vandalising door entry systems to ground floor flats".

In addition, the council used the powers to try to find out who was stealing from a tip and to monitor a property from which it thought drugs were being dealt.

On four occasions the powers were used to see if fishermen were gathering shellfish from a prohibited area in Poole harbour.

Council officials have said the surveillance lasted on average for two weeks for the purpose of "preventing or detecting crime or for preventing disorder".

Tim Martin, head of legal and democratic services at the council, said: "Illegal shellfish dredging can cause harm to the conservation of stocks in the harbour and could also lead to a potentially serious public health risk if illegally fished stock is not fit for consumption."