This episode was long considered lost, but was later found and included on the authoritative BFI DVD release of the series in 2019.
This special holiday episode was the pilot for the new series to begin after the new year. It was broadcast on December 26, Boxing Day in the UK, thus the title.
This episode actually aired on 4 January 1968. According to the booklet for the BFI's 2019 DVD release, and to Michael Palin in a retrospective interview on the discs, it was due to air on 26 December 1967, but due to a mistake at Redifussion, the official first episode was broadcast instead.