When JK Rowling conjured up the tales of Harry Potter in her imagination, did she gaze into a crystal ball like Sybill Trelawney, Hogwarts’ eccentric professor of divination, and picture the adventure taking place just outside Watford?

The Warner Bros. Studios in Leavesden – once an old aerodrome where Rolls-Royce turned out aircraft engines – was home to the Harry Potter film franchise for a decade.

Now it’s an ideal setting for perhaps the hottest family attraction in Britain as sound stages J and K have been transformed into Warner Bros. Studio Tour London – The Making Of Harry Potter.

When we arrived at the studio, we queued excitedly by a recreation of Harry’s cupboard under the stairs and filed into a cosy room where video screens recapped the success of the books and films.

We took our seats in the airy cinema next door for a light-hearted filmed introduction hosted by lead actors Daniel Radcliffe, Emma Watson and Rupert Grint.

As the actors disappeared into The Great Hall and the lights came up, the cinema screen rose to reveal the very same gargantuan wooden entrance – an impressive flourish to begin the day.

Before tackling the rest of the tour at our own pace, our guide revealed that 15 golden snitches were concealed around the tour and she encouraged us to scrutinise every inch of the sets to find them.

A couple of snitches were hidden rather sneakily, so parents may need to lend a roving eye to junior treasure hunters.

From The Great Hall, we made our way around the first sound stage which included the Gryffindor Boys’ Dormitory, where Harry’s brown suitcase rested snugly beneath one of the beds, and Dumbledore’s Office, which is decorated with 48 portraits of former Hogwarts headmasters.

Interactive elements are limited and for the most part though, this tour is hands-off: look but don’t touch.

Leaving the first sound stage, we emerged into an open-air back lot which includes Hagrid’s motorbike and a 22ft-tall triple-decker purple Knight Bus, as well as recreations of Number 4 Privet Drive and the burned-out cottage in Godric’s Hollow.

Inside the second sound stage, we marvelled at intricate prosthetics and creature models from the special effects workshop, and brought a mandrake to life at the touch of a button.

Passing beneath an 18ft-wide animatronic model of Aragog the spider, dangling ominously from the ceiling, we suddenly felt cobblestones beneath our feet and knew at once we were heading on to Diagon Alley.

The detail in this gargantuan set is astonishing and we spent nearly 20 minutes peering through the windows of Slug & Jiggers apothecary, Flourish & Blotts book shop, Eeylops Owl Emporium and Ollivander’s Wand Shop.

A room devoted to the art and design department, filled with concept drawings, paintings and architectural models, leads on to a stunning, hand-sculpted 1:24 scale model of Hogwarts Castle.

As we circled the model, almost 50ft in diameter, lighting effects cycled through day and night every four minutes, drawing attention to 300 fibre optic lights, which simulate the lanterns and torches of students passing along hallways.

For details of Warner Bros. Studios Tour, call 0845 0840900, or visit wbstudiotour.co.uk.