The show took its name from the message (frequently seen on the TV screen in those days) which was displayed when there was a problem with transmission. Although originally conceived as a children's programme, it quickly acquired a cult crossover following amongst many adults. Indeed quite a lot of material could be considered adultish. In aiming at a family audience it is similar to The Goodies.
This was an early appearance of many actors and comedians who later became famous: David Jason, Denise Coffey, Graham Chapman, Eric Idle, and others. The Bonzo Dog Doo-Dah Band performed a song in each programme and Bob Kerr's Whoopee Band also appeared. The programme comprised a series of sketches, often bizarre and surreal, frequently satirical, a disjointed style which was to become more famous in the subsequent and more daring Monty Python's Flying Circus; at least one sketch was re-used in the Python series. Strange animations between sketches were crafted by the then unknown Terry Gilliam, who also graduated to Python - his `Christmas cards' animation reappearing there. Factual dispute: `Christmas cards' was made in black and white, Python was in colour, and I'm pretty sure that `Christmas cards' did not appear in Python. Part of Christmas cards did appear in Python, but not the whole animation, as far as I remember it was the "joy to the world" segment.
One long running segment of the show was Captain Fantastic, featuring a parody superhero (Jason) in improbable adventures against Mrs. Black (Coffey).
In common with another important Monty Python predecessor, At Last the 1948 Show, many episodes were wiped despite their importance to the history of British television comedy, and the surviving episodes are seldom seen.
Need to check the full cast list