Google has been caught tracking smartphone owner's whereabouts even when they have switched off their location services.

The tech giant has been gathering and sending addresses of devices running the Android operating system without users knowing, even if they do not have a SIM card inserted or any apps installed, an investigation by Quartz has found.

It is well known that phones can pinpoint their surroundings while the location services are turned on, in order to use when they are using Google Maps or apps that need geographical information to function.

But Google has been collecting the addresses of telephone masts that are "pinged" by phones since the beginning of this year, it has emerged.

The release of this information could put victims of domestic abuse and potential criminal targets like celebrities at risk if someone was able to hack into their phones. The practice raises privacy concerns for the two billion people using the operating system - the largest in the world.