This was on the Martin Lewis bit on TV last week and I just stocked up on a load of books for party bags and for presents. Basically buy 10 or more books from a long list and you only pay £1 per book.
shop.scholastic.co.uk/10-books-for-10
There are extra discount codes too that work on top of the £1 offer plus across the whole of the Scholastic Book sale (I also got some Roald Dahl books for £2.99 each for example.)
I spent more than £30 so entered JAN165 and got £5 off but you can get £10 off orders over £50 if you put in JAN1610 (but even I couldn't spend that much on children's books!)
Thought I'd pass it on. I'm looking forward to a big box of books arriving! Happy shopping!