Various characters were shown watching or listening to Enoch Powell's infamous "Rivers of Blood" speech. The speech was made on 20 April 1968 to the General Meeting of the West Midlands Area Conservative Political Centre. The speech was partly recorded for television, but wasn't broadcast live. Gently also refers to Dr. Martin Luther King in the past tense. King had been assassinated earlier in the month on April 4.
The quotation cited during the episode, "Whom the gods would destroy, they first make mad," was first spoken in English by Prometheus in Henry Wadsworth Longfellow's poem "The Masque of Pandora" (1875).