It was the start of a new adventure when Harry, Hermione and Ron got onboard the Hogwarts Express each school year, and with the old steam locomotive now rolled up at Leavesden’s very own Platform 9 3/4, visitors can now begin theirs.

This week, Warner Bros. Studio Tour London - The Making of Harry Potter offered the Watford Observer a sneak peek at its new exhibition expansion, which includes Platform 9 ¾ and the original Hogwarts Express steam train.

The 78-year-old red engine has returned to the series' production home, displayed on a realistic set of tracks with steam billowing, ready to greet visitors later this month and offer them the chance to climb aboard the train's carriage and to pose with a luggage trolley as it disappears through the platform wall.

Following the announcement in January, work has continued to ensure this new, permanent 20,000ft2 expansion is ready for opening in just less than two weeks time.

Hosting the preview event were train enthusiast Mark Williams, who plays Arthur Weasley in the film franchise and Academy Award winning and BAFTA winning, special effects supervisor John Richardson.

Alongside his never-ending love for the Harry Potter films, Mr Williams' interest in trains has been demonstrated in his involvement in television programmes about the industrial revolution and locomotives.

He said: "I've really enjoyed being back at the Studio Tour, seeing the original Hogwarts Express and the superb recreation of Platform 9 3/4. People don't always realise that the school train was in face a real working locomotive which has been transporting passengers up and down the country since 1937.

"The train is a worthy addition, and once again it's a great piece of confidence from Warner Bros. to bring a 75 tonne engine into a purpose built 9 3/4 - it just shows how strongly they feel about the Harry Potter films.

"I never got to go to Hogwarts on the Hogwarts Express - of course I would have done when I went to Hogwarts originally! But there was always a great sense of occasion during filming with it, because the locomotive itself brought a real sense of excitement because it was the beginning of each adventure."

The Hogwarts Express engine and carriage was used for exterior shots, but the majority of the interior scenes were filmed on a soundstage at Warner Bros. Leavesden.

The scenery going by the train was shot by the second unit crews and then composited into the green windows by the Visual Effects Department.

The VFX team also created other effects seen out the windows, like frost, Chocolate Frogs, Dementors and flying Ford Anglias.

Mr Richardson, who was very much a part of that team, explained that Leavesden was very much his home now, and that he jumped aboard the chance to get involved with the new tour expansion.

He said: "I've never been away from Leavesden. We were here doing movies for 10 years and then as soon as we finished the films I still had a workshop here. So we kept the workshop on to build all the things to go into the tour.

"Even today I've still got a workshop over on the studio side. We build all the new things to put in the tour there, including all the rigs for this train for instance.

"As soon as it was decided to extend the tour and put the train in I got involved in designing the steam effects, to make it look although it was hot and steaming and ready to leave the station.

"Throughout all of the films we had the Hogwarts Express, and wherever we filmed it - we filmed it probably in five different locations - we always had to make the steam look right for the movie. So we were always working with the train or around the train then to do this."

A selection of prop luggage will also be on show for visitors to enjoy in the new recreation of Platform 9 3/4, with the addition of a train-themed souvenir shop.

The new section will open to the public on Thursday, March 19 and entrance will be included in the standard ticket price.

Click here to see our picture gallery from the preview day.