Keith is a minicab driver who, between fares, relates how his marriage broke down and his wife, Marion ran off with a work colleague, Geoff. Later he is employed as a chauffeur for a movie producer (of sorts) who's wife is rich and he continues to try and see his children and be friendly with Marion.
The reason for the two separate plot strands is simply that the series started life (on TV) as a series of 10 minutes shows but then was given half an hour per show later. The strength of the show is that it easily fills 30 minutes or 10 or even an hour. The show takes place entirely in the front of Keith's car from a single camera mounted on the dashboard. We never see anyone else apart from Keith, we only hear about them. This sounds boring why in the age of gross out comedy and high speed shows like 24 etc would anyone want to watch what is essentially a monologue?
Well, simply because the writing is superb. We only have Keith's point of view but we get to find out what is really happening. Keith is kind to everyone and totally naive he tells things in the best light he can, which is funny because we are able to read between the lines and see what is really going on. Once Keith begins to tell his tragic tales of the mundane you can't turn off, I am always hooked to the end and never get bored. Like all good British comedy this has an air of despair about it and it is quite depressing, I would be lying if I said it was hilarious, because the dark side off sets this quite often. However just like Basil Fawlty and David Brent are funny and sad little men at the same time, so the comedy is here not over-confident, brash `don't go there' type humour like the US can do so well, but low key, tragic comedy.
Brydon is fantastic in the character he has created over years. If you see him interviewed he is so the opposite of Keith it's hard to believe when watching the show it is so easy to forget he is acting at all. Few people could hold the attention of an audience when they are the only thing onscreen for the whole show and it is a credit to both the writing and Brydon's delivery that he can do it.
Overall this show is very hard to describe and it is NOT a laugh a minute, hilarious comedy. Rather it is a tragic comedy where the whole thing feels funny and sad at the same time and, as a result, you will be amused but not roaring with laughter all the time it is more than that. If you can see it on TV then do so, but otherwise it is well worth finding on DVD.