The police have wrongly accused and detained two people in separate cases as a result of mistakes made in the disclosure of their personal communications data, a watchdog has revealed.

The mistakes made by phone and internet companies responding to requests from the police were not realised and had very significant consequences for the two members of the public who were wrongly detained/accused of crimes as a result, said Sir Paul Kennedy, the official interception of communications commissioner.

His annual report reveals there were 895 "communications data errors" reported to his office, arising from 494,078 requests for the confidential details of internet and mobile phone use made last year by the police, security services and other law enforcement agencies.

The disclosure will fuel the debate over safeguards in the government's draft communications data bill, known by critics as the snooper's charter, which will require phone and internet companies to extend the range of records they keep to include use of Twitter, Facebook and other social media.

Kennedy also discloses that 141 local authorities made a total of 2,130 requests for internet snooping data in 2011, an increase from the previous year's figures. He said most local council requests involved trading standards operations, and his inspectors had disclosed a fresh case under which data secured under the Regulation of Investigatory Powers Act was used in 2009 to prove whether or not a parent lived in a particular school catchment area.

It followed a widely publicised case a year earlier in which Poole council in Dorset used the Ripa powers to spy on a family to see whether they lived close enough to an oversubscribed school. The commissioner said the fresh case was "extremely regrettable" and communications data should only ever be used to prevent or detect crime, but he said it would be wrong to use it as evidence that local authorities were frequently using their powers inappropriately.

He said it was the first and only such case uncovered by his inspectors out of the thousands of local authority requests they had looked at since 2006. The home secretary, Theresa May, has announced her intention to block local authority access to communications data for trivial purposes.

The annual reports of the three separate surveillance commissioners covering official phonetapping, human and covert surveillance operations and the use of communications data show that the overall number of requests from law enforcement agencies fell in the past year.

David Cameron said they showed that the powers were being used properly. "There have, regrettably, been breaches and errors in the use of these powers. While these have been few in number relative to the overall number of applications, the government is not complacent. The causes of these breaches and errors will need to be addressed," he said.

Rachel Robinson, of the campaign group Liberty, said: "This report shows the dangers of government plans to make phone and internet companies hold even more records on the communication and browsing habits of the whole population. The scale of surveillance revealed is alarming, but worse still is that hundreds of errors subjected the wrong people to targeted surveillance by public authorities.

"That two innocent people were wrongly detained and accused of crimes as a result of these blunders should make the government think again about turning us into a nation of suspects rather than citizens."

Kennedy said that in the vast majority of the 895 cases in which there were errors, the mistakes were realised and the wrong acquired data destroyed. In most cases the mistakes involved asking for confidential data on the use of a wrong telephone number or internet address.

"Unfortunately in two separate cases where a communications service provider disclosed the incorrect data, the mistakes were not realised and action was taken by the police forces on the data received. Regrettably, these errors had very significant consequences for two members of the public who were wrongly detained/accused of crimes as a result of the errors," Kennedy said. "I cannot say more … as investigations are ongoing."