Alex Mayer’s write-up of his The Elder Scrolls: Oblivion-based partial re-creation of Britannia circa Ultima 9 is in German at the Planet Skyrim website, but a rough translation of it reads thusly:

This plugin brings the world Britannia from the venerable Ultima series back to life, and is based primarily on Ultima 9 Ascension, though it is not a 1:1 copy of the world. You can visit places like Britain, Paws, Buccaneer’s Den, and discover many more.

Note: The Mod clearly belongs in the category “Beta”, and is incomplete in every way; there is no story, no dungeons interiors, no NPCs or new objects. In addition, only part of the world is modeled. As well, the mod is anything but “clean” (see readme). I would like to point out that I’m not going to continue working on the mod (school stress, lack of time …) and I therefore will set it free, for others to change or work on. Perhaps there are still a few Ultima fans and eventually a full-fledged Britannia Mod…

I’m assuming he ends with something like “can be created one day” or some such. Be that as it may, herein you’ll find Alex’s re-creation of at least part of Ultima 9’s Britannia. And based on the above screenshots, I’m assuming that you can expect to find a quite decently high quality rendering of our favourite continent therein.

So, you know…project entry, download…you know the drill by now.