EA Games is the most successfull publisher, though i think it's borken into various development houses.
I think Rockstar must make a few bob from the GTA games in particular, and they're from Scotland, too

! (Dundee - hence the word 'Quine' in Vice City). Codemasters, Eidos and DMA are Scottish too IIRC. So are Mucky Foot, though they're not so famous (Startopia, Blade II). And a guy who graduated from my uni started up a development company - they made an early PS2 title called 'Airblade' or something, I think - although they may be 'rupt now.
NB: Rare posted record losses fairly recently.