Microsoft announced the GSP initiative in an attempt to ease governments' concerns regarding the security of its products, claiming that the shared information will help them protect national software infrastructures more efficiently.
The programme, which is based on Microsoft's shared source initiative launched in 2001, covers access to code for Windows 2002, XP, Server 2003 and CE, and has often been viewed as a reply to open source rival Linux.
Under the programme, government representatives can visit Microsoft's campus, view millions of lines of source code, use analysis tools, simulate threats to assess vulnerabilities and even create new versions of Windows based on Microsoft material.
The UK is the third signatory. Russia became the first country to announce it had joined the programme last month, whilst NATO was the first international government agency to join the scheme.
Andrew Pinder, the UK's so-called e-Envoy was recently asked to take on the new role of Central Sponsor for Information Assurance (CSIA) for the UK government.
In this latter capacity, Pinder signed the agreement with Microsoft. He said that the programme will be "key to the risk management of the national infrastructure," and that he will seek similar agreements with other software makers.
"By allowing us access to their source-code we will be using the knowledge gained, together with the rest of our experience, to make sure that a greater range of products meet the UK government's information assurance needs."