@cheong: No, there's no excuse. Vista and IE7 were released 7 years ago. That's plenty of times to fix what is an important (and I can't imagine particularly challenging) website. This isn't some corner shop outfit, it's a national government.
EDIT: Although most corner shops probably have better IT systems than the UK government anyway...
FYI, I've finished a government project in HK in 2009 that targets WinXP+IE6 only. The project development lasted for 2.5 years and procurement process last about half year if I didn't get it wrong. And you don't expect the government allocates fund for the "next stage" project when the "new" one just go live right? And all "software development" budget has to be added in the annual budget of corresponding department submitted in Feb,
Say we allocate the required budget next Feb, risk challenge from auditing to shorten the procurement process to 3 months, and assume it's trival development so only need a development time of 3 months + 3 months UAT (you rarely see governement project with development time lower than 3 months because it'll be too risky for them, and there would be not much profit for the project), the earliest estimate if nothing goes wrong would be we'll see a new website by Nov 2014.