I have to admit I haven't read the book myself, but I've been told it is very good. The synopsis in the Mirror says:
"Mildred Hubble is a trainee at Miss Cackle's Academy for Witches, but she's making a mess of it. She keeps getting her spells wrong, and crashing her broomstick."To get your copy of the book, which is published by Puffin, you have to buy today's Daily Mirror, cut out a coupon and take it along to Martin's or Toys R Us stores.
The Mirror is giving away a different Puffin children's book each day this week. On Monday it is giving away The Hodgeheg (Dick King-Smith), followed by The Werepuppy (Jacqueline Wilson), Mr Majeika (Humphrey Carpenter), The Hundred-Mile-An-Hour Dog (Jeremy Strong), The Diary of a Killer Cat (Anne Fine) and Milly-Molly-Mandy Stories (Joyce Lankester Brisley).
According to the Daily Mirror website, the coupons will be repeated next Sunday and you can also claim your books by post if there isn't a shop stocking them near you.
To find out more about the offer, visit the website: http://www.mirror.co.uk/news/top-stories/2010/01/31/7free-puffin-books-115875-22007683/
If you miss out on the offer, you can buy copies of The Worst Witch through Amazon for £3.47.