So it should be, (even if it was racist, which it isn't) it's just an accurate rendition of how people spoke then. The one thing you could never accuse the show of was racism, right from its first series it was always about showing London as a proudly multicultural place, and Del as someone who treated everyone equally. They have black and Asian people as just other colorful characters in the show, in contrast to many contemporary sitcoms where ethnicity was still played for cheap laughs. It does really annoy me that sitcoms, even all time great ones, are treated in such a shoddy way, where they can just be chopped up and messed around with like they weren't important cultural artifacts. We'd never do the same with books and plays.