Councils used anti-terror laws to monitor residents flouting planning laws, litter bugs and even their own employees.

Surveillance operations were mounted by officials at Bristol and North Somerset councils more than 150 times over the past five years, records reveal.

Local authorities were given powers that were originally only used by police and the security forces to help in the fight against terrorism.

But admissions that officials have used them to check up on residents who commit minor offences such as dropping rubbish has sparked furious claims they are operating a "snoopers' charter".

The Liberal Democrats, who uncovered the information, called for major curbs on who can use the Regulation of Investigatory Powers Act (Ripa).

Local government spokeswoman Julia Goldsworthy said: "This Government sees civil liberties as little more than a temporary inconvenience. Slowly but surely, freedoms have been eroded.

"We're now in a situation where dog fouling is considered enough to warrant surveillance by council officials. Unless the law is reformed, it risks becoming a snoopers' charter. Surveillance powers should only be used to investigate serious crimes and must require a magistrate's warrant."

Bristol City Council has used the power 132 times to monitor residents it believes have dropped litter or been involved in anti-social behaviour, fly-tipping and fraud.

According to Freedom of Information records, North Somerset Council carried out 33 operations, including one over planning rules and another that involved monitoring an employee. No records were available for South Gloucestershire and Bath & North East Somerset .

Local Government Minister John Healey has written to councils to warn them Ripa should not be used for minor crimes.

A city council spokesman said: "Surveillance is necessary to tackle fly- tipping in some cases – particularly as the offence is often carried out secretively at night and the culprit leaves no evidence as to where that waste has come from.

"The public are outraged at the way a tiny minority dump waste and fly-tip in and around this city and they expect us to use the powers we have to act where we can, which is what we try to do where it is reasonable and legal to do so.

"We don't use Ripa powers in every case and we make a careful assessment of where its use is necessary and appropriate."

A spokesman for North Somerset Council said: "The council carries out investigations ranging from trading standards to licensing and benefit fraud. Sometimes these investigations will require the use of surveillance.

"The report we received following the Office of Surveillance Commissioners visit in June 2008 was complimentary and the Inspector and Chief Surveillance Commissioner were satisfied with the overall arrangements in place at North Somerset Council.

"We are confident that our low-level use of surveillance is both fair and proportionate."