HM Treasury is the latest government department to join Flex, the public sector shared services network run by supplier Fujitsu.

The department said its IT systems were at the end of their life and needed to be upgraded.

Flex offers the option of sharing desktop hardware, software and services between departments, saving on money and energy use.

Currently 10 Downing St, the Cabinet Office, the Children and Family Court Advisory Support Service and the Office of National Statistics have signed up.

Fujitsu will also be providing support and maintenance facilities over the five year contract.

Karen Delafield, chief information officer for the Treasury, said the contract will benefit the department in many ways.

"The partnership will deliver significant efficiencies while also providing a level of flexibility and scalability which cannot be achieved by maintaining services in-house," she said.

"It also enables us to participate in the government shared service in line with our own operational efficiency programme.”

The Treasury said IT staff affected will be transferred to Fujitsu under Transfer of Undertakings (Protection of Employment - TUPE) regulations. The department says it has been in discussions with unions since December 2008.