The fourth Harry Potter story broke all publishing records by selling 372,775 copies on its first day, according to authoritative figures yesterday.

The total - described as "amazing" by the market research group Whitaker BookTrack - netted the author JK Rowling nearly £300,000 in extra pocket money and shrivelled the achievements of recent bestsellers like Hannibal Lecter and Delia Smith.

The records overtaken by Harry Potter and the Goblet of Fire were nearly all set by Ms Rowling's three earlier Potter books.

Spurred by unprecedented publishing hype, the new story sold in a single day - last Saturday - nearly two-thirds of the total achieved by its predecessor, The Prisoner of Azkaban, in the last five months of last year.

Ms Rowling can count on a further boost in income when sales figures for yesterday and Monday come through from supermarkets like Tesco. Most of these stores get no wholesale deliveries on Saturdays, so that the publisher Bloomsbury's strict embargo on sales meant they could not get copies on their shelves for the weekend.

Goblet of Fire's total sales figure covers not only purchases at bookshop electronic tills but sales on the internet and through newspaper offers.

Total sales in bookshops alone were 256,246. These were more than half the 503,473 copies of the first Harry Potter story, The Philosopher's Stone, sold in the whole of last year. The next story, The Chamber of Secrets, sold 417,171 in 1999. The Highway Code - regularly king of bestseller lists till Ms Rowling came on the scene - sold 393, 396 in that year. Thomas Harris's third Lecter novel, Hannibal, sold 58,319 in its first five days last year. Delia Smith's How to Cook, Book 2, sold 110,425 in its first three days last December.

Internet and newspaper sales made up more than 116,000 of the book's first day total. Britain's biggest internet bookseller, Amazon, yesterday claimed some 65,000 of these, adding: "Thousands of orders are still coming in every day".

According to the Society of Authors last night, writers get an average 8% royalty on each hardback copy sold. Goblet of Fire is being sold at an average of £10. On this arithmetic - assuming that she has not by now negotiated a higher personal royalty - Ms Rowling was £298,220 better off on Saturday night.