Two members of the public were arrested by police and wrongly accused of crimes because officials wrote down the wrong numbers, a watchdog revealed today.
Sir Paul Kennedy, the Interception of Communications Commissioner, said two forces were given the wrong information by a communications service provider (CSP) which led to two people being wrongly detained and accused of crimes last year.
The firm was also slow to report the errors and initially gave unsatisfactory explanations as to how they occurred or what was being done to prevent it happening again, Sir Paul said.
"In two separate cases where a CSP disclosed the incorrect data, the mistakes were not realised and action was taken by the police forces on the data received," he wrote in his annual report for 2011.
"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.
"I cannot say more about these two instances at this time as investigations are ongoing."
Some 42 per cent of the errors made last year were caused by acquiring data on the wrong communications address, he said.
He added: "This type of human error usually occurs due to the transposition of digits in telephone numbers or internet protocol (IP) addresses."
While the mistake was realised "in the vast majority of cases", these two errors were not noticed before action was taken, he said.
Sir Paul went on: "In these cases the CSP was slow to report the errors and I was not initially satisfied with the explanations the CSP provided in relation to how the errors occurred, or the measures they put in place to prevent recurrence.
"I am pleased to say that this CSP has since put in place some very sensible measures which will hopefully prevent recurrence of similar errors in future.
"Fortunately errors with such severe consequences are rare."
A total of 895 communications data errors were reported last year, with a fifth of these made by CSPs and the rest by public authorities.
"I am satisfied that the overall error rate is still low when compared to the number of requests that were made during the course of the reporting year," Sir Paul added.
But Prime Minister David Cameron told MPs the Government was not complacent and "the causes of these breaches and errors will need to be addressed".