Britain’s smallest mobile network, Three, has gone to war with regulators, seeking its customers’ help in a campaign over the upcoming auction of mobile airwaves.

The operator, owned by the £37bn Hong Kong conglomerate CK Hutchison, is to ask customers to deluge Ofcom’s chief , Sharon White, with letters urging her to impose tighter restrictions on BT and Vodafone.

Last week the telecoms regulator announced that it intended to bar BT from bidding for a portion of the radio spectrum right due for sale next year.

However, Three chief executive, Dave Dyson, who had demanded more radical action to curb the biggest players in the market, is angry that Ofcom did not go further, and is pushing hard for all operators to be barred from owning more than 30pc of the airwaves.

A 30pc limit would effectively force BT, which together with its mobile arm EE currently owns 42pc of available UK wavelengths, to sell off some of its rights. At the same time Vodafone, on 29pc, could not seek to gain a greater share of mobile spectrum in future.