"coupling" theme music

I know the theme music to the television series “Coupling” is the song “Perhaps, perhaps, perhaps.” While watching last night, one of my friends whom I’ve just introduced to the show -swears- that song is lifted from somewhere else, but can’t remember where and it’s driving her nuts. Now, granted, it’s kind of fun to watch her go nuts, but in the end I think we’d all be a lot happier if someone could point out if, indeed, this music is lifted, and if so, from where? Thanks in advance.

It’s been covered a million times but the best known version is by Doris Day.

I never knew the Doris Day version, I just have heard it by Cake.