They downloaded emails, text messages, photographs and documents from wi-fi networks as they photographed virtually every British road.

It is two years since Google first admitted stealing fragments of personal data, but claimed it was a ‘mistake’.

Now the full scale of its activities has emerged amid accusations of a cover-up after US regulators found a senior manager was warned as early as 2007 that the information was being captured as its cars trawled the country but did nothing.

Around one in four home networks in the UK is thought to be unsecured – lacking password protection – allowing personal data to be collected. Technology websites and bloggers have suggested that Google harvested the information simply because it was able to do so and would later work out a way to use it to make money.