Bradford Council has secretly monitored members of the public and its own staff more than 500 times in the past five years – an average of around twice a week.

And in the last 18 months powers, which have been dubbed a “snoopers’ charter” by critics, were used 37 times to try and catch out Council staff thought to be defrauding the authority.

It has led to action being taken against 12 employees, with one being prosecuted for theft, others being given written and final warnings, and four suspended pending disciplinary hearings over “potential gross misconduct for dishonesty”.

Legislation under the Regulation of Investigatory Powers Act 2000 (RIPA) was expanded in 2003 and made available to all local authorities. It allows the Council to use covert surveillance, such as CCTV, monitoring equipment, including audio, video, cameras and binoculars and staff going undercover.

The Council’s own policy states RIPA can be used “in the course of investigating frauds, breaches of legislation or regulation and in the interest of the safety and well-being of the district”.

Instances include the videoing of unlicensed premises being used as a slaughterhouse, CCTV monitoring of fly-tipping hotspots, officers following suspected benefit fraudsters, and secret filming and photographing of planning breaches.

Staff have gone undercover on two occasions in recent years posing as passengers to detect unlicensed cab drivers. The last one took place the weekend before Christmas, when nine private hire drivers were caught illegally plying for hire and were stripped of their licences.

In the past five years the powers have been used 533 times in total, the majority in environmental protection cases such as fly-tipping and noise nuisance. In 2006/07 this figure increased to its highest at 237 cases in one year. But 201 cases relate to monitoring noise nuisance – and the Council has since been advised to stop using covert surveillance. The number then drops in the following year.

Speaking of the blip in results, Ian Bairstow, strategic director for environment and neighbourhoods, said: “The Council only uses covert surveillance as a last resort and will use overt methods whenever possible.

“The figures over the last six years show that the use of covert surveillance is dropping, and was used on only 20 occasions in the past nine months.”

Bradford Council leader Councillor Kris Hopkins said: “It is not a secret that the Government brought in this legislation. What we need to do is use the existing legislation that is out there appropriately to go in pursuit of individuals who are potentially breaking the law.”

Coun Ian Greenwood, leader of the Council’s Labour group, said: “I have some concerns about an act that was brought in for anti-terrorist purposes being used on a regular basis for other things.

“I certainly think that rules and guidelines should be in the public arena and subject to public debate.”

Coun Jeanette Sunderland, leader of the Council’s Liberal Democrat group, said: “I think it is right and appropriate that the Council uses the power to investigate people who are fly-tipping and people who are involved in illegal activities.

“The powers in Bradford aren’t being used to make a fast-buck – they are being used to investigate fraud and illegal activity.”