The "I'm sorry I'll read that again" team (headed by the ever-present Angus Prune) were not merely funny. They were also to go on, in various guises, to television careers in Monty Python's Flying Circus (John Cleese) and the Goodies (Graham Garden, Bill Oddie) and as such, for fans of either of those shows, this tape is actually a small piece of comedy history.
A mixture of (very good-natured) satire, farce, brain-extrudingly bad puns (such as in Escape from Colditz, where one of the guards, "Hans Boompsadaisy, is uncle to a girl named Ann -- Hans's niece Ann Boompsadaisy... you are right, ve Germans have no sense of humour....") and some of the silliest songs you will ever hear... no, I'm sorry, I've forgotten what I was going to say.
In addition there are regular irregulars in the cast, such as the terrifying (but adventurous) Lady Constance (instantly recognisable by her warbling mating-call).
The old ISIRTA material is definitely as important to the prehistory of Monty Python in its own way as "Do not adjust your set" is in its. Serious scholars of comedy cannot afford to be without at least one of their cassettes. This is a time capsule of sixties weirdness.
It is also so funny it will make you sneeze.