Episode 41 Michael Ellis (1974) begins with the opening theme song, followed by a screen that says "THE END," followed by the end credits, and then the show begins. This was to allow the unusual ending of that particular episode which would have been ruined by the closing credits.
In episode 23 Scott of the Antarctic (1970), the opening segments take up so much time that the theme song doesn't play until about 20 minutes into the show.
Depending on the content of the individual shows, the credits were changed accordingly, often appearing in anagrams (Tony M. Nyphot's Flying Risccu), with a different title completely (The Buzz Aldrin Show (1970)) or with strange additions to the names of the cast and crew, such as various foodstuffs, sex toys and political gambits.
Several episodes go on for several minutes following the closing credits. Some closing credits even incorporate the BBC "rolling earth" logo that was used at the time between programs.
One episode omits the entire opening sequence of "Monty Python's Flying Circus" in favor of a simple title caption - The Cycling Tour (1972).
In Royal Episode Thirteen (1970) John Cleese doesn't open with "And now for something completely different". Instead he says Queen Elizabeth II will be watching and the show begins with entirely different opening sequence and song. At the end the audience and characters stand as "God Save the Queen" is played over end credits.
On some occasions, the opening credits do not occur until many minutes into the program -- sometimes as late as the half-way point in the show.