IT WAS included in the pack of the greatest American films given by President Obama to Gordon Brown on his recent White House visit. The Library of Congress has deemed it ‘culturally significant’’ and it is believed to be the most watched movie of all time.

‘It’ is The Wizard of Oz, the story of Kansas farm-girl Dorothy Gale and what happens to her in the fictional land of Oz, after her home is blown away by a tornado. And it is 70 years old this year.

But if you thought it was just a charming tale of witches and wizards and a little girl who wants to go over the rainbow then think again. There is much more to this story than meets the eye.

The original novel upon which the film was based is now regarded by some as a parable about the economic depression of the late 19th century, which occurred just before L Frank Baum’s story was published in 1900.

Co-incidentally – or maybe not – the film starring Judy Garland was released during the Great Depression of the 1930s, its themes of good and evil and vanquishing monsters apt for the gathering Nazi menace, which was about to trigger the Second World War.

Baum was writing at a time when prices had fallen by about 22 per cent, causing debt, and among those particularly badly affected were farmers who set up the Populist political party to represent their interests and those of industrial labourers.

The US was then operating on the gold standard – a monetary system which valued the dollar according to the quantity of gold held by the government. The Populists wanted silver, along with gold, to be used for money. This would have increased the US money supply, raised price levels and reduced farmers’ debt burdens.

According to US high school teacher Henry Littlefield, who wrote a book about the story’s possible significance in 1964, the characters take on a political guise.

He suggested that Dorothy represented Everyman, the Scarecrow represented the farmers, the tin man an industrial worker and the Lion a character who backed the silver cause. Who was the wizard? ‘American Presidents’, apparently.

The film cut out many of these themes but took on its own myths and significances.

Dorset-based movie expert Anwar Brett, who edits the magazine Focus on Film, says even the use of Technicolor told its own story.

“The film starts off in the Depression era in black and white but bursts into rainbow colours; red for the slippers, green for the witch, yellow for the road,” he says. “It returns to black and white as the filmgoers would have to have left the fantasy world of the cinema, to go back to their ordinary lives.”

Despite the on-screen camaraderie there was, he says, much rivalry between the established stars such as Ray Bolger who played the Scarecrow, and the younger Garland, who was aged 17.

And there was an even darker side, with allegations of sexual debauchery among the Munchkin actors and even an enduring myth – which sparked the Trainspotting writer Irvine Welsh to write a play based upon it – of a lovelorn Munchkin hanging himself on set and his corpse appearing in one of the movie’s scenes.

The International Wizard of Oz Club (yes, there is one) rubbished the claims, pointing out that for someone to successfully take their life in this way on a busy set would be impossible.

“I don’t think it’s true, either,” says Brett, “But the fact that people even bother to make up and spread myths about this film shows how big it has become.”

Other myths include the claim that Pink Floyd’s album Dark Side of the Moon is an alternative sound-track to the movie (it apparently makes for interesting watching in tandem with the CD) and fortune-teller Professor Marvel’s coat actually belonged to the story’s author L Frank Baum.

The important thing to remember, says Brett, is that the film was released in 1939, what many consider to be the greatest year for movies ever. “When you look at the year it came up at the Oscars, it was against the stiffest competition ever recorded,” he says. “Gone With The Wind, Ninotchka, Goodbye Mr Chips, Stagecoach, Wuthering Heights, they were all battling with the Wizard for best picture.”

It may be 70 years old but those who love it wouldn’t bet against it lasting for a good 70 more.