Eh? What about Quicken 2004?
My research found nothing you could upgrade to from any UK version of Quicken - I was particularly looking for a route from Quicken 2000, as I said (I bought this one because they improved Y2K behaviour), but if there had been an "upgrade to Quicken 2004 first, then you can upgrade to so-and-so" route I'm pretty sure I would have found it.