Privacy International is planning to file a criminal complaint with the UK police over Google's interception of private Wi-Fi data.
The move comes after Google published an audit by third-party computer forensics experts into how the data interception happened, according to the Financial Times.
Privacy International said the report indicates that the interception was deliberate and therefore contravenes UK wiretapping laws.
Police investigations are already underway in Australia and a similar investigation is under consideration in Germany, where an audit by privacy authorities forced Google to admit its Street View cars were collecting Wi-Fi data as well as images.
But intentional interception of Wi-Fi data violates laws in at least half the 30 countries where the data was gathered, Simon Davies, director of Privacy International told a conference in London earlier this week.
Google has gone about gathering this data in the wrong way because it did not take the privacy element seriously enough, said Davies.
Any plan to gather, store and use personal information is bound to run into problems, he said, if it is not done openly and transparently, and does not have a clear benefit to those involved.
Google has claimed that the interception of the data was unintentional and caused by inclusion of experimental code by mistake in software used by the Street View cars.
But the third-party report alleges that the code was deliberately set to store private data, which is a violation of the UK's Regulation of Investigatory Powers Act, said Davies.
Privacy International's complaint is expected to be filed by early next week.