Penelope Keith does not actually appear, but her voice can be heard talking to Jerry when he's talking to Tom and Barbara from his bedroom window.
During the end credits roll it is just possible to hear Richard Briers and other cast members chatting to each other as they (presumably) take applause from the studio audience.
Jerry and Tom began work at JJM Limited at the same time, eight years earlier.
The first episode starts on the day of Tom's 40th birthday.