Some of these British characters I'm not familiar with but aren't half of these characters "personas" thus no actual nationalities?
They are mythical figures of the British Isles so they could be considered from Britain.
Of course if we stick to human characters (not counting Football Managers and Total War series), we only got five (and Indonesia got none).
I think
Capcom has more Britain human characters.
There are already six just from fighting games alone : Titanic Tim, Eagle, Birdie, Cammy, Jon Talbain, and Dudley.
Not SEGA characters, but their games are playable in SEGA console.