Mahoney was actually born and raised closer to Manchester England than Jane Leeves, whose character was supposed to be from there.
The other fact was that Mahoney wasn't really old enough to be Grammar's father. Hence the cane.
We might also mention David Angell, one of the show's creators, who died in 9/11. The other two producers are still around.
So both Leeves and Mahoney had English accents in real life? I never heard a hint of it at all on the show. Pretty impressive.