Monster Munch was launched in Britain in 1977 by Smiths. Originally called “The Prime Monster” (a play on “The Prime Minister”, and as part of a wider campaign), the decision was taken to rename the snack “Monster Munch” in 1978. Advertised as “The Biggest Snack Pennies Can Buy” – in reference to the large size of the crisps – each pack featured a different monster on the front of the packet.
The snack was supported by a “Monster Munch Club”, whose members received a “Monster Munch Munchers” membership pack which included a membership card, pen, several story books, and a story tape which included six “tall stories” and accompanying songs.
Info gleaned from Wikipedia