Blue Peter actually has a really good survival rate, most stuff from the mid-1960s onwards survives. Whilst this is perhaps partly forward thinking on the part of Editor[1] Biddy Baxter, AFAIK it was partly so older material could be reused in later editions to save money.

[1] The title of the "showrunner" of Blue Peter, so in the meaning of "editor of a newspaper", not "videotape editor".