Preview of the about-to-open Harry Potter studio tour

The Harry Potter franchise may have drawn to a close - and JK Rowling moved on to the world of adult fiction - but Warner Bros are not about to let their billion-dollar boy wizard fade away.

The latest money-spinner is the Harry Potter Studio Tour, offering fans a behind-the-scenes look at how the films were made.

Yesterday [Wednesday] The Daily Telegraph was granted a preview of the attraction, which is expected to draw 5,000 visitors a day when it opens on March 31.

While young Potter fans will delight in seeing the original sets, props and costumes close up, parents should brace themselves for an expensive day out. Child tickets are pounds 21 and a replica of Professor Dumbledore's robe in the gift shop costs an eye-watering pounds 495.95.

The setting is Leavesden Studios near Watford, Herts, not a place synonymous with film star glamour. The exhibition is housed in a former aerodrome and factory where all eight films were made over the course of a decade.

Visitors can wander down the cobbles of Diagon Alley, inspect the table settings in the Great Hall at Hogwarts and peer into the cupboard under the stairs at Privet Drive where the young Harry was forced to sleep. There is a refreshment stall serving "butterbeer", in reality a sickly sweet concoction of toffee-flavoured cream soda.

The sets look as wonderful up close as they did on screen, although they are cordoned off behind ropes. The highlight is the meticulously-created model of Hogwarts School, scaled down to 1/24th of life-size, which was used in the exterior shots for the first films. It took six months to build and is testament, as with everything else on display, to the skill of the British production designers.

Videos explain how the films were made, from the Quidditch stunts to the visual effects which removed Ralph Fiennes's nose for his role as Voldemort. Some details take away a little of the mystique: those dusty tomes on Dumbledore's shelves, for example, are phonebooks covered in leather.

At pounds 21 for a child aged 5-15, pounds 28 for an adult and pounds 83 for a family of four, prices are comparable to the likes of Alton Towers but definitely on the expensive side considering there are no rides and the tour can be done in a couple of hours.

As with most modern tourist attractions, the set-up requires visitors to exit via the gift shop where there is a bounty of merchandise on offer.

The cheapest item is a pounds 3.95 lollipop. A polyester Hogwarts scarf costs pounds 24.95, a plastic Horcrux ring is pounds 39.95 and a replica of Harry's broomstick is pounds 249. An audio translation for foreign visitors adds pounds 4.95 to the ticket price.

Leavesden is only half an hour from London - 20 minutes by train from Euston to Watford Junction (not, alas, by Hogwarts Express) and then 10 minutes on a special Harry Potter-themed bus.

Boris Johnson, Mayor of London, is a supporter of the project. "The venue will bring Potter as close to London as possible, which is where he belongs - not Orlando," he said, referring to Universal Studio's Harry Potter theme park in Florida. "It is a chance to show the world that we do this kind of thing as well as Hollywood."

In fact, the only real disappointment comes as you approach the studios. When you have an image in mind of Hogwarts' fairytale spires, pulling up outside an aircraft hangar near Watford's branch of Carpetright destroys a little bit of the Potter magic.