After a gap of 5 years since the last episode "Summer", the story continues in real time 5 years later.
In the 2004 Christmas episode, Richard Curtis was going to name all of Alice and Hugo's children - the names included Hagrid and various Teletubbies.
Frank reveals that he was born on August 12th 1929, making him 75 in this episode. The date is also John Bluthal's, the actor who plays Frank, birthday.
David says that Alice is 'looking depressingly healthy'. Ironically, Emma Chambers died of a heart attack in 2018, aged just 53.