The government has signed a deal with Microsoft to provide Windows XP support and security updates across the whole UK public sector for 12 months after regular support for the operating system ends on 8 April.

The agreement is worth £5.548m, and covers critical and important security updates for Windows XP, Office 2003 and Exchange 2003, all of which have reached end of life in Microsoft's normal product cycles.

The deal has been negotiated by the new Crown Commercial Service (CCS), set up within the Cabinet Office to act as a single public sector-wide purchasing and commercial operation. The extended support is available to all of central and local government, schools and the NHS.

According to Sarah Hurrell, commercial director for IT and telecoms at the CCS, the contract has saved at least £20m, compared with individual departments negotiating their own deals. She said it made no sense for each organisation to pay separately to have access to the same security fixes, when each patch could be made available across the public sector to everyone who needs it.

"This allows us to have continuity for eligible public sector organisations as they migrate to other operating systems," she said.

One condition for any public sector body wishing to take advantage of the extended support is that they have a "robust plan" in place to move off Windows XP, Office 2003 and Exchange 2003 within a year.

"This is a 12-month breathing space," said Hurrell. "No one wants to be on an end-of-life infrastructure. We will make sure people have plans that stand up to scrutiny."

Hurrell would not provide details of how many public sector desktops and laptops still run Windows XP. Independent estimates by Netmarketshare.com suggest that 27% of all desktops worldwide still run XP, but Hurrell would not say if government use is above or below that figure.

However, 85% of the approximately 800,000 PCs in the NHS still ran XP as of September last year, according to research from EHI Intelligence.

"The NHS is very grateful for this deal," said Hurrell.

Larger public sector organisations with more than 250 Windows XP users will also need to have a premier support agreement in place with Microsoft -- Hurrell suggested that most already have -- but smaller organisations will receive support without needing the additional service.

"We will plan with Microsoft to make sure that support is easily accessible," said Hurrell.

Originally launched in 2001, Windows XP is Microsoft's most successful operating system, and in many private and public organisations has survived subsequent versions of Windows such as Vista, 7 and 8.

Rob Wilmot, crown commercial representative for software at CCS, said: "We are delighted that this agreement will deliver projected savings in excess of £20m against standard pricing in the next 12 months. By combining demand, on behalf of central government departments and the wider public sector, Crown Commercial Service has demonstrated the benefits of government working as a single customer to achieve best value for the taxpayer, while continuing to build good working relationships with our technology suppliers."

Microsoft said that the new deal should not mean that public sector bodies put off plans to migrate away from the older software products.

"Many organisations have made good progress in moving to a modern desktop operating system and have successfully mitigated the risk that running Windows XP will bring. However, some organisations will not have moved off Windows XP by 8 April," said a Microsoft spokeswoman.

"We have made an agreement with the Crown Commercial Service to provide eligible UK public sector organisations with the ability to download security updates to Windows XP, Office 2003 and Exchange 2003 for one year until April 8 2015. Agreements such as these do not remove the need to move off Windows XP as soon as possible."