Asda and Tesco have reported magical sales of the final instalment in the Harry Potter series, Harry Potter and the Deathly Hallows, which went on sale on Saturday.

Asda, which slashed the price of the book from an RRP of £17.99 to just £5, said it had sold 450,000 copies between midnight and 4pm on Saturday.

Tesco, which sold the book for £5 if customers spent £50 in store, said it expected to have sold 350,000 copies in the first 12 hours, but a spokesman told the Daily Mail that it had soon become obvious that it had underestimated demand.