...from: http://arstechnica.com/microsoft/news/2010/08/despite-petition-uk-government...

UK government: Upgrading away from IE6 costs too much By Emil Protalinski | Last updated a day ago The UK government is not yet interested in ditching Internet Explorer 6, saying the costs required to do so outweigh the benefits. Six months ago, an online petition started in hopes that the UK would abolish all use of the world's most-loathed browser.

The petition debuted soon after the German and French governments began to advise their citizens to use a different browser than IE in the wake of the Chinese-Google hack attack. It closed on June 6 after gathering 6,223 signatures; on July 30, the government gave an official response. Here's the crux of it:

Complex software will always have vulnerabilities and motivated adversaries will always work to discover and take advantage of them. There is no evidence that upgrading away from the latest fully patched versions of Internet Explorer to other browsers will make users more secure. Regular software patching and updating will help defend against the latest threats. The Government continues to work with Microsoft and other internet browser suppliers to understand the security of the products used by HMG, including Internet Explorer and we welcome the work that Microsoft are continuing do on delivering security solutions which are deployed as quickly as possible to all Internet Explorer users. The UK government is correct in saying that Microsoft will continue to keep IE6 updated and secure. In fact, the software giant has promised to do so until April 2014, which is when Extended Support for Windows XP (which includes IE6) ends.

That said, Microsoft trash talks IE6 every chance it gets, promoting the increased security of IE8 at the same time. Furthermore, as IE flaws are discovered, IE6 and IE7 are affected more often than not, while IE8 usually remains unaffected.

The true reason the UK government doesn't want to upgrade becomes clear in the last paragraph of its explanation. It doesn't want to spend the money:

It is not straightforward for HMG departments to upgrade IE versions on their systems. Upgrading these systems to IE8 can be a very large operation, taking weeks to test and roll out to all users. To test all the web applications currently used by HMG departments can take months at significant potential cost to the taxpayer. It is therefore more cost effective in many cases to continue to use IE6 and rely on other measures, such as firewalls and malware scanning software, to further protect public sector internet users. On some level, this makes sense; not every benefit is worth the costs. But such testing will have to be done eventually, and not even Her Majesty's Government can stick with IE6 indefinitely.