The scene with Paul (Paul Casar) and Phil (Simon Farnaby) (aka Simon and Garfunkel) has references to two Simon & Garfunkel songs - "Bridge over Troubled Water" and "The Sound of Silence".
The characters known as Simon & Garfunkel are actually called Peters (Paul Casar) & Lee (Simon Farnaby) in the series.
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.