The number of Transport for London (TfL) staff using their own phones and tablets to access company information has risen sharply over the past three years, a Freedom of Information (FOI) request has revealed.

The organisation, which oversees London Underground's 150-year-old rail network and London Buses, has 583 personal devices registered under its bring-your-own-device (BYOD) policy, up from 106 in 2010, 242 in 2011 and 430 in 2012.

However, with 28,000 staff across TfL, the relative number of employees at the organisation using their own devices for work purposes remains low.

TfL CIO Steve Townsend, subject of a CIO profile earlier this year, said: "We will be equipping more staff with the latest mobile technology, such as tablet computers which will improve the information they can give to customers on the move. We take personal security management extremely seriously and ensure that each device has a unique password. We regularly analyse our authorised user database to ensure that our network is not at risk."

The data obtained by network automation provider Infoblox under the Freedom of Information Act also reveals what devices TfL staff are using.

The iPhone was the most popular device, with its 320 users outnumbering Samsung's 87 and Android's 70. Apple claimed second place as well with 178 iPad users, compared to just eight Surface users and one Asus owner.

Only two Motorola and two Nokia devices were in use, while 22 staff used BlackBerry phones - three more people than those who owned an HTC device.

Last month Townsend said that he wants to see the connectivity on London Underground improved, adding that the organisation is testing a number of communication technologies, including on-train WiFi.