When Lance discloses to Andy who Kate is, and goes on to describe his summer love twenty-plus years ago, Andy says "Tell me more, tell me more, was it love at first sight?" He's quoting a line from the song Summer Nights by John Travolta and Olivia Newton-John from the musical Grease.
Toby Jones (Lance), Mackenzie Crook (Andy) and Simon Farnaby (Art) also appeared in Christopher Robin (2018) together as Owl, Newspaper seller & Taxi driver respectively.
Laura Checkley (Louise) & Alexa Davies (Kate) also worked together on Cradle to Grave (2015) as Lil & Yvonne respectively.
The characters known as Simon & Garfunkel are actually called Peters (Paul Casar) & Lee (Simon Farnaby) in the series.