I’m a big fan of Cabin Pressure too. All the episodes are on YouTube as it’s worth starting from the beginning with them. I’d say in fact that the episode Ottery St Mary is one of the funniest 30 minutes I’ve ever come across on either radio or TV.
John Finnemore, the writer, also has a great sketch show on Radio 4, and regularly appears on the Now Show. There’s a clip of him on YouTube absolutely destroying the News of the World.
Also agreed re Hut 33. very funny. And Andy Hamilton’s Revolting People and Old Harry’s Game are also superb.
Radio 4 (and Radio 4 Extra for the old stuff) is in fact probably the best quality comedy anywhere.