Actor Allusion: In two different sketches in Series 3 and 4, both Mitchell and Webb explicitly make references to Peep Show, which of course stars the two.
Accidentally Correct Writing: The sketch featuring a fake advert for the alcoholic sports drink "Glucozade Port" (a parody of Lucozade Sport) becomes this when you realise the original name of Lucozade was called Glucozade when it was first released, which is implied the writers of the sketch weren't aware about this fact.
Additionally, when the show first aired, viewers were able to enter a competition to win the actual clarinet prop from the "Green Clarinet Man" sketch. The competition allowed participants to come up with a new useless sidekick à la BMX Bandit from the well known "Angel Summoner and BMX Bandit" sketch. The winning entry was revealed to be Yo-yo Lad.
Hide Your Pregnancy: Subverted with actress Olivia Colman for Series 2, whose prominent belly was visible no matter what sketch she was in. While it was brought up in one sketch, but they didn't really try and hide it either. Not hiding it made at least one sketch Darker and Edgier than it was originally intended to be written, which involved Colman's heavily pregnant character being strangled to death by her husband.
Keep Circulating the Tapes: When Series 3 and 4 aired on TV, viewers could access the extras of the show via BBC Red Button, featuring animated sketches from the radio series (with two animated by famous British animators David Firth and Edd Gould), behind the scenes footage, interviews and unseen sketches. While some of the animated sketches and unseen sketches were already on YouTube, some of the other content didn't see the light of day when the series stopped airing. However, all of the Red Button extras were available online starting from June 2018.
No Export for You: In the US, the show ran for a period on Netflix and Hulu, and it hasn't been made available there since those streaming runs ended.
Real Song Theme Tune: The theme song is a slightly edited version of "Alive & Amplified" by The Mooney Suzuki.
The corner store set from the "tremendous thirst" sketch was reused in the "Biscuit Telekinesis" sketch.
The house from the Coverage of People Buying a House and then Living in It sketch was reused in the "Green Clarinet Man" sketch.
Throughout the "Jet Pack" sketch, while Webb's character is interviewing Mitchell's, several people are shown with the aforementioned product flying through the sky. As revealed by "behind the scenes" footage on the Series 4 DVD, these people are in fact the crew members of the show, including the producer.