When Richard Coyle read for the part of Jeff, he spoke in a Welsh accent. The character wasn't written Welsh, but the producers liked it and hired him. It wasn't until well into the second series that they realized that Coyle was not Welsh, just putting it on for the show.
NBC's adaptation of the show was considered such a sure thing that when the second season UK original was released on DVD in the States it featured a sticker reading "The original UK version of the SMASH NBC hit!". Unfortunately the DVD came out the very same week that the US version was canceled.
Richard Coyle (Jeff) chose not to return to the show for season four. Coyle was afraid of being typecast as Jeff and wanted to explore other roles. He was replaced by Richard Mylan as Oliver, a nervous comic book store owner who pursues Jane. Jeff "returns" in the final episode played by a different person.
Though some scenes are shot away from the studio audience (the nude scenes for example and exteriors) no "canned laughter" is used. The scenes are played on monitor for the studio audience and their reactions are real.
Director Martin Dennis provides most of the voice-overs required for the series. A few notable exceptions are "The Melty Man" (performed by Richard Coyle) and the radio announcer who introduces Jane in "Jane and the Truth Snake" (Ben Miles).
In season 4, during a usual bit of wackiness, Steve comments that this kind of thing doesn't happen as "this is not an American sitcom". In fact, there was an extremely short-lived American version of the series (Coupling (2003)) that was abhored by viewers and critics alike, resulting in the show's cancellation after only four episodes.