I have just come across this, I think it is a glitch on the site so get in as fast as you can!
Go to the site and search for Things to make for Mother's Day book, its a bright pink usborne activity book.
Add it to your basket (or as many as you like, you can order up to 20) and it comes up £0.00
All you pay is £3.50 standard delivery charge!
It must be a glitch in the system but hurry before they deal with it!!!