Mobile operator Three has announced that its four million contract mobile phone customers have more than doubled their monthly data use over the last year.

Three, which is the UK's smallest mobile operator but claims to carry 50% of the country's mobile data traffic, said that its average contract customer uses 1.1GB of data each month, up from 450 megabytes last summer.

iPhones and Android smartphones are the most data-hungry, with many customers using up to 1.5GB per month.

Unlike some mobile operators, which cap the amount of data their customers can use, Three offers unlimited data packages.

“Price plans that remove the fear of going over a data limit enable demand to grow as consumers are free to discover just how much they can do on the move,” said Dave Dyson, chief executive officer of Three.

“Even I don’t understand how much data I use on a daily basis so it’s no surprise that having an all you can eat worry-free data package is proving to be so popular with our customers.”

The news backs up a report by the communications regulator Ofcom, released last week, which found that the overall volume of mobile data consumed has doubled in the 18 months to January 2012.

Ofcom estimates that the average UK consumer now spends ninety minutes per week using a mobile to access the internet, largely replacing their use of PCs and laptops for watching video clips and sending messages.

“Simply put, mobile data usage is like a bottomless pit, it’s expanding all the time,” said George Wareing, head of mobile and broadcast, Virgin Media Business.

“People aren’t going to give up this trend for streaming content and all the indications are it’s going to increase. Operators need to think about the long-term impact and put in place a strategy that’ll make sure customers aren’t affected by a potential bottlenecking of services.”