Internet giant Google has been threatened with criminal proceedings by the information watchdog after further personal data unlawfully collected by its Street View cars was discovered.
The Information Commissioner's Office (ICO) has handed the US multinational an enforcement notice demanding that it destroy four discs containing information it took from unsecured WiFi networks.
Google had previously pledged to destroy all data collected in this manner - but admitted last year that it had "accidentally" retained the additional discs.
The ICO has warned Google that failure to comply with the legal order will be considered as contempt of court, which is a criminal offence.
Stephen Eckersley, ICO head of enforcement, said: "The early days of Google Street View should be seen as an example of what can go wrong if technology companies fail to understand how their products are using personal information."
Google admitted in 2010 that it had collected information, such as passwords or emails, from unsecured wireless networks as its vehicles roamed residential streets to create the mapping product. In November 2010, the ICO ordered Google to destroy all data obtained in this way but in February 2012 the company discovered further discs of UK data that had not been deleted.
The ICO then reopened its investigation following a report by America's Federal Communications Commission that an engineer deliberately wrote the software to capture the information and shared his work with the entire Street View team. The ICO understands the additional discs had been kept in "quarantine cages" and had not been accessed.
The watchdog has ordered the company to destroy the additional data within 35 days and demanded that any further Street View vehicle discs holding personal data and collected in the UK are immediately flagged. It concluded that the detriment caused to individuals by the most recent breach failed to meet the level required to issue a monetary penalty.
But campaigners said Google had escaped with a "slap on the wrist". Nick Pickles, director of privacy campaign group Big Brother Watch, said: "People will rightly look at the UK's approach to this issue and ask why, given regulators in the US, Germany and other countries have fined Google for exactly the same infringement, it is being allowed to escape with a slap on the wrist in Britain. Is our privacy somehow less worthy of protection?"
A Google spokesman said: "We work hard to get privacy right at Google. But in this case we didn't, which is why we quickly tightened up our systems to address the issue. The project leaders never wanted this data and didn't use it or even look at it. We co-operated fully with the ICO throughout its investigation and having received its order this morning we are proceeding with our plan to delete the data."