This story involves actors in a TV series based on the books of "Kent Finn", the best-selling author (and love rat) played by Adam James in Game (2017), the first episode of Season Four; Finn and his fictions are also mentioned in the later episodes Lazaretto (2017) and Muse (2018).
The burnt remains of a £20 note are found near Hugh Sellers's body - an especially brutal taunt made by rich and over-privileged youths to a man who has nothing. It has long been strongly rumored that burning a high-denomination banknote in front of a homeless person was one of the initiation ceremonies required for membership of the Bullingdon Club, the notorious real-life university society for Old Etonians whose former members include Tory Prime Ministers David Cameron and Boris Johnson.
When David Astin is first seen behind the counter of his joke-shop, he is made-up and costumed to resemble a character in "Mr. Benn", the animated TV series for children popular in the 1970s (and already referenced in the "Scherzo" episode in Season 8).
Quite apart from the obvious allusions to "A Clockwork Orange", the depiction of the over-privileged Oxford bully-boys also shows them in blazers and straw boaters, clutching teddy-bears - a reference to Sebastian Flyte and his dubious friends in Evelyn Waugh's 1948 novel "Brideshead Revisited" (not to mention the famous 1981 television adaptation).
The episode of "Jolly For Short" excerpted in this story appears to be based on the "Jolly" novel which author Kent Finn is reading aloud to an audience of fans at a book launch at the start of the "Endeavour" episode of several seasons earlier entitled "Game". That episode is set in early 1968, this one a little over four years later in the summer of 1972. The giveaway is that in both instances, a fictitious character named "Eduardo Sanchez" is mentioned (as a murder victim). This is also the name of one of the real-life directors of "The Blair Witch Project".