Britannia Software Ltd is a british company that made a couple of ZX Spectrum games between 1983 and 1986. One of their later Spectrum titles, Play Your Cards Right, was also advertised for the C64 and the "Amstrad, Spectrum" (which may refer to Amstrad's Spectrum models, not to CPCs).
For the CPC, they produced the Britannia ROM Board, and ROM utility called Super Romplus - Auto Rom Control System 1.6 (1986).