Escalator etiquette in most countries tends to match the rules of the road. In New York and Taipei, motorists and escalator users keep to the right, while in Singapore and Tokyo both keep to the left.

So why do passengers on the London Underground stand on the right-hand side of escalators when the rules of the road dictate that we drive on the left?

The mystery has been solved by a silent film from the 1920s that has been restored recently for The Times BFI 53rd London Film Festival.

A visual joke in Underground, the first film to use extensive footage of the Tube, shows how the design of early escalators meant that it was important to step off with the right foot.

Times Archive, 1911: Tube improvements: the escalator system

Test runs of the first example of the continuous moving stairway built for railway service in this country are being made at Earl's Court

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Unlike modern “comb” escalators, where the end of the moving stairway is at right angles to the direction of travel, older “shunt” escalators ended with a diagonal so that the stairway finished sooner for the right foot than for the left.

The idea was to allow passengers to keep their left foot on a moving stairway as they stepped off with their right.

Passengers who chose not to walk down the escalators were asked to stand on the right so that anyone wishing to overtake them at the end would be able to take advantage of the extra section of moving stairway.

Anthony Asquith, the son of Prime Minister Herbert Asquith, who became famous in his own right for directing films such as Pygmalion and The Browning Version, decided to use the escalator design for comedic purposes by showing a soldier dithering over how to get off.

The sequence shows the soldier looking worried as he sees a sign that reads: “Step off: right foot first.” He looks over his shoulder at his commanding officer, who would have insisted that soldiers always begin marching with their left foot. In his confusion, he stumbles and is thrown forward with his kit bag.

Simon Murphy, a curator at the London Transport Museum, said that historians had assumed that the rule about standing on the right was an arbitrary decision but the Underground footage suggests otherwise.

“It’s a good theory and it’s probably true,” he said. “It’s all down to whether or not you think someone thought through all of this — but most of the time they did think things through in detail. They made scale models of stations, so they thought hard about passenger flows.”

When shunt escalators were replaced by comb escalators from 1924 onwards, the rule stayed in place and continued to mystify foreigners who expect British people to overtake on the right, as we do on roads.

The first escalator in Britain was installed in 1898 in Harrods, but it was their introduction to the Tube 13 years later that exposed them on a wide scale.

When Underground was released in 1928, most Londoners were familiar with escalators but Asquith was the first film director to make them an important part of the plot.

In one scene, a London Underground employee prevents a rival from pursuing a woman by tripping him up on an escalator and then delaying him by dusting him down.

Footage in Waterloo station suggests that habits have changed little since the 1920s. Men take seats ahead of women while one man irritates a fellow passenger by reading his paper over his shoulder.

Underground will receive a gala performance as part of The Times BFI 53rd London Film Festival on Friday at the Queen Elizabeth Hall.

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