The sheer scale of the Potter phenomenon has transformed the industry, and not everyone has been a winner. The release of Harry Potter 5 boosted the quarterly revenues of Amazon by 40 per cent, but these kind of profits can cause ruthless price-cutting by the big chain booksellers and supermarkets. Since 1997, the Booksellers Association says the number of independent bookshops has declined by about a quarter, with a boom in chain bookshops leading to a slight overall increase in numbers.

GLASSES

Harry was bullied in younger years, so he knows the taunts that used to face playground spectacle-wearers. No longer: many opticians reported that sales of glasses to under-16s rose by 40 per cent after Potter. Some people asked for frames when not needed. “We hear a lot from parents, how much easier their children find it now that Harry Potter has made glasses cooler,” the Royal National Institute for the Blind said. Dollond and Aitchison is licensed to sell Potter look-a-like frames.

TOURISM

Why do tourists flock to eat at an average Chinese restaurant in Edinburgh? To pay homage to the place where J. K. Rowling wrote most of the first Potter book — when the Buffet King was the coffee shop Nicolsons. Other places to see a big leap in visitors: Alnwick Castle in Northumberland, the film version of Hogwart’s School; “Hogwart’s Express”, or rather the Jacobite steam train across the Glenfinnan Viaduct, and Goathland station in North Yorkshire, where Harry alights.

BOARDING SCHOOLS

Boarding school treasurers have been keenly awaiting the next Harry Potter. In 2000 the number of girl boarders went up for the first time in 20 years, and rose for another two. But then the boom burst in 2003 — caused by a lag in the release of Harry Potter 3? — and the trend has been down since. Boarding places fell by 1.4 per cent last year.

BROOMS

The Nimbus 2000 flying broomstick is, to muggles, a hazel and birch sweep called a besom. This ancient but vanishing British craft has now been revived by the film — and the handful of surviving “broom squires” (broom- makers) have received orders from all over the world. “The game of Quidditch has been brilliant for the besom,” said Adam King, one of the last broom squires.

FIRST EDITIONS

Although ubiquitous, the Harry Potter books have transformed the collectors’ market. The first editions of the original book are the most prized as the print run was in the hundreds, and these fetch £20,000. A 13-year-old from Fife sold a first edition of the second Potter book for £3,500. The preliminary drawing of Harry Potter for the first cover sold for £85,750.

SINGLE PARENTS

No sooner had J. K. Rowling become a millionaire than she wrote a cheque to the charity One Parent Families for £500,000, followed by the same amount in 2002. She has criticised the way single mothers are derided by politicians. “Single parents feel tremendously grateful to her for standing up to them,” said the charity. “I don’t think it’s an exaggeration to say she has really changed attitudes.”

TREES

J. K. Rowling insisted that the million copies of the Canadian edition of Harry Potter and the Order of the Phoenix be published on recycled paper. Under her influence, Bloomsbury has said that Harry Potter 6 will be printed partly on paper deemed “ancient forest-friendly”, the first British bestseller to do so. It is thought that 96,000 trees will be saved by the UK edition alone.

HELEN RUMBELOW

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy