A secret 'spy in the sky' scheme has been revealed which allows officials to pinpoint the exact location of thousands of vehicles with satellite navigation systems - and it could be the first step into a national road pricing scheme.
The secret 'Big Brother' operation is built into the small print of a contract between the Department for Transport and the satnav company Trafficmaster.
The controversial scheme monitors some of the 50,000 drivers who have Trafficmaster's Smartnav system.
But, critics fear, the system could provide the blueprint to monitor the location, speed and journey details of millions of drivers in years to come.
Such a system might be used to manage a system of road pricing, where motorists are charged according to which roads they use and the time of day. It might also be used to identify speeding drivers.
However, the DfT stresses that all the information is anonymised to ensure they do not have the personal details of drivers