http://www.colorschemeeditor.com/index.php?p=schemes&lang=EN
The first download link is for a zip file of all of the original built-in schemes (or close approximations of them)
It lists the Brittanica scheme as 'britania.clr', but I suspect that's just a typo.
(As was the original naming by TomTom - it should really be "Britannica" with one T and two N's if it's named after the Encyclopaedia etc!)
Can I also recommend the "GB_New" scheme, near the bottom of that same page? That's the one I always use. There are also UK-Alt and UK-OS (ordinance Survey colours) too.