Their first album is self-titled--full of witty lyrics and elegant musicianship / composition. Mumps is from their second (and last) studio album The Rotters' Club, which I prefer to the first by a bit.

They were an early Canterbury supergroup, with members from Delivery, Matching Mole, Egg, Gong, and Caravan. They later evolved into National Health. Rather than providing you with background, I'm afraid I've just given you more bands to research.