If all you want is UK/ROI, you'll find it cheaper than the full European map set. At any rate, I think that all are at 925, or are about to be in a day or two. I haven't been following the release schedule closely enough, but they're due.
To purchase a new map, you'll want to use TomTom Home to work the magic. If you don't have a current version of that on your PC, let us know what you're using (PC or Mac) and we can point you to a current copy at TomTom for download.