I first encountered Rocky Road Crunch Bars in Starbucks - simply divine with an Americano. Nigella Lawson popped up with a recipe of her own in her boook Nigella Express. As the book's title may suggest, all recipes are easily and quickly made, and the crunch bars are no exception. It is a fridge cake so no baking is required.
Sourcing the mini-marshmallows proved troublesome, but in the end I found them available from large Sainsburys branches. The Rich Tea biscuits can be from the 'Value' range of products and are very cheap.