Harry Potter and the Deathly Hallows has thrown off concerns over internet spoilers and broken embargoes to confirm its position as the world's fastest-selling book today, with Nielsen Bookscan estimating a staggering 2.7m copies sold in the UK of the seventh and final book during a hectic period of just 24 hours - a 35% increase on first-day sales of JK Rowling's last blockbuster, Harry Potter and the Half-Blood Prince.

The figure, which includes sales through UK bookshops, supermarkets, internet sites and newspapers on Saturday July 21 2007, brings to a close a remarkable run for the popular children's serial, which saw record-breaking sales of 1.8m copies in one day for the fifth book in the series, and 2m for the sixth. UK sales of the Harry Potter series as a whole now stand at 22.6m copies, with 72.1m copies sold worldwide.

Supermarket sales appear to account for around half of the 2.7m copies, with Asda's quick apology to Bloomsbury and aggressive price-cutting producing sales of 126,000 copies priced £5 in the first hour, and 485,000 copies in the first 24 hours - a rise of 128% on figures for Harry Potter and the Half-Blood Prince.

According to a Tesco spokesman, the chain sold "more than 500,000 copies over the weekend" at an in-store price of £10 - a price which reduces to £5 as part of a supermarket spend of £50 or more - and are continuing strongly. "We're expecting that people will put it in the trolley along with their weekly shopping," he said.

Sainsbury's refused to give precise figures, claiming that sales were commercially sensitive information, but suggested that sales at £8.87 have "gone very well".

Of the major booksellers, Borders and WHSmith are both "very pleased" with sales over the weekend. Both refuse to give figures for sales in the UK, though Borders reports 1.2m copies sold worldwide - "considerably up" on last time - and WHSmith claims sales at a rate of 15 copies a second.

Waterstone's are less tight-lipped, quoting 350,000 copies sold in the first 24 hours. The high-street chain is celebrating the success of Potter-night parties in 279 branches, with 100,000 books sold at £8.99 each in the first two hours after the book's release at midnight last Friday.

According to Waterstone's Jon Howells, the chain was selling 20 copies a second at the height of trading.

"We estimate a quarter of a million people visited our stores for the midnight openings," he said. "At our Piccadilly store launch - we're now calling it 'the People's Potter Party' - we had over 7000 people come along, and we did not close the store until nearly 4am. When it opened again at 8am there was another queue already formed."

Many other branches reported queues of more than 1,000 people, he added, with the queues that formed outside two separate Edinburgh stores becoming so long the two queues combined.

"I was at the Piccadilly store for the duration," he continued, "and it was the best night I've had in nearly 20 years of bookselling - everyone was fabulous, the fans who in some cases queued for days, and the booksellers who did 24 hour shifts then were back on Saturday morning after only a couple hours' sleep.

"Harry Potter may go to school at Hogwarts, and may occasionally get lost in with the cornflakes and cat food, but Friday night and Saturday morning saw him return to his true home, the bookshop."