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Fed up with the grand claims of the country's big four mobile phone operators, the government's telephone watchdog has stepped up its efforts to oblige them to increase investment in the network.

Its latest weapon - a publicly available interactive network coverage map which, the Autorité de régulation des communications électroniques et des postes (Arcep), says is accurate to within 50 metres.

It is the first time such a level of accuracy has been made available to the public, France Inter says.

The map - - allows internet users to compare the true quality of each operators' mobile network. Users can enter an address, and see in an instant the level and quality of coverage available from Orange, Bouyges, SFR and Free - including whether it is possible not just to make and receive calls, but send and receive text messages or even log on to the internet.

It has been rolled out nationwide following a successful trial in the New Aquitaine region.