The problem is that you simply cannot spec a project that size. Rather than trying to design a central system what you should do is spec the interchange formats. In other words copy the one system known to work at the required scale - the web - rather than trying to design a one size fits all. This is much simpler, and allows for much greater flexibility within different parts of the service. It also allows for planned future expansion and progressive deployment. The NHS is far too complex to do it any other way and have it actually work. But of course, the people who come up with these insane ideas don't know the first thing about IT, not even how to procure it. As a professional system designer this makes me furious on more levels than I care to think about.