Basil the Rat (a.k.a. Rats) - S2-E6
Trivia: Melody Lang, who plays Mrs. Taylor in this episode, is Andrew Sachs' wife.
Basil the Rat (a.k.a. Rats) - S2-E6
Trivia: In some shots of this episode, a real rat was used. These shots were pre-recorded due to the production team having concerns that it could run into the studio audience.
Answer: It's "Leisure Complex" by Dave Gold and Gordon Rees. Can be found on YouTube. The relevant clip is around 25 seconds in.