Ofcom is warning that it may take action against O2 if the mobile operator fails to successfully rollout 3G phone services.

The regulator has ruled that the five companies holding a 3G licence must make their networks available to 80 per cent of the UK population. The original deadline was 31 December 2007, but O2 is currently only at 75.7 per cent, a shortfall equivalent to 2.5 million people.

The company now has until the end of June to address this deficit. If it fails to reach the goal, Ofcom will reduce the term of its 3G licence by four months.

The other four licence holders are H3G, Orange, T-Mobile and Vodafone.