Mobile phone operator O2 today announced that it has expanded its recently launched 4G network so that it covers a quarter of the UK population. 

The high speed mobile internet service - made available just nine weeks ago in London, Leeds and Bradford - is now accessible by 15 million people, according to O2.

Since its 4G launch, the Telefonica-owned operator has rolled out the service to 11 major cities and over 90 other towns in the UK, from Paisley to Sevenoaks.

O2 said the 4G service, which went live in Manchester last week, will be switched on in Edinburgh, Newcastle, Wetherby and Huddersfield in coming weeks.

O2 is aiming to catch up with EE, which has already rolled its 4G network out to approximately 60 percent of the UK population and is available in 131 UK towns and cities. 

O2 said that in the last 12 months customer demand for data has increased by 50-75 percent. “In our first week of launching 4G, data traffic on our network rose to a level that took our 3G service the equivalent of three years to clock-up,” the company wrote on its website.

O2 also said it is investing £1.5 million every day on replacing and upgrading equipment to meet this rising demand.

Vodafone and Three, the remaining mobile operators in the UK, also have their eyes on the 4G market. 

Vodafone's 4G network was launched on the same day as O2's and by the end of the year it should be available in Birmingham, Bradford, Coventry, Edinburgh, Glasgow, Leeds, Leicester, Liverpool, Manchester, Newcastle, Nottingham and Sheffield.

Meanwhile, Three plans to launch 4G in four UK cities before Christmas.