So, inspired by this Pinterest pin of Ali's, I decided to make some instead. I had a Cath Kidston catalogue, and I had some double-sided sellotape, and I had a pair of scissors (paper scissors NOT fabric scissors - I get very twitchy about appropriate scissor use).
It could not be easier. Stick the tape onto the catalogue and trim. Then stack the lengths of tape into an old syrup tin and photograph. When you are ready to use your washi tape, just peel off the backing and stick on to whatever you like.
What are school holidays for if not for wasting time fiddling about with paper and sellotape? Coming soon...washi tape strips made from newspaper, or takeaway menus - I think that could look really cool.