The company says this growth is driven by its smartphone focus and a nationwide programme to upgrade its network.
Its network, designed for data-hungry users, uses DC-HSDPA technology, which is supported by the iPhone 5, the Sony Xperia T and the Windows Phone 8X by HTC, as well as the iPad mini and iPad. Three says some of its users are already reporting peak speeds over 20Mbps.
39 per cent of the population already has access to it, 50 towns and cities including Blackpool, Glasgow, Nottingham and Southend on Sea. The company says the network will reach more than half of the UK population by the end of this year, with 80 per cent of the population covered by April 2013.
Three's acquisition of 2x15Mhz of radio spectrum at 1800Mhz for its deployment of 4G next year doubles its overall spectrum capacity and provides further room for customer growth.
Dave Dyson, Chief Executive of Three UK, said: “These network improvements are designed to maintain our position as the fastest growing UK mobile operator. Our Ultrafast network is giving more people in more places access to an even faster mobile internet experience.”