A WOMAN subconsciously playing with her hair is a sure bet; stand to one side of a couple holding hands; avoid people with heavy books; secretly check the angle of a handbag.

Follow these tips, and your chances of grabbing a newly vacated seat on an overcrowded Tube train will shoot up, according to a book dedicated to that fine art.

Other tips include using a make-up mirror to check for vacant places behind you, knowing which school uniforms belong to which schools and learning where the big company headquarters are to predict a sudden exodus.

The guidance appears in Sit Down on a Commuter Train!, a tome written for Japan’s millions of beleaguered commuters that is selling out fast as the hot weather approaches. A comfy seat under the air conditioners will soon be priceless. But the book, based on a scientific study of passenger behaviour and body language, is equally pertinent for Britain’s rail and Tube users. It lists all the subtle signs that suggest that those with seats are about to get up and leave.

It includes charts, diagrams and complex equations for calculating the likelihood of finding a seat in a variety of different circumstances.

The book began as a printworker’s blog. Hajime Yorozu posted daily rants on the internet about his failure to find seats. “If you have been on a Tokyo commuter train just once, you have experienced Hell,” he told The Times.

Finally, he realised that there might be a solution to grabbing vacated seats. “Watch people’s eyes very closely,” he says. “Glances at a watch or station name are promising signs. People about to leave their seats will generally tend to uncross their legs, move their bags upright on their laps, or search in their pockets for a bookmark.”

Apparently, women in Japan groom themselves for most of the journey to work — therefore a woman who has arrived at the final task of fixing her hair is almost certainly getting ready to disembark.

Another giveaway is how commuters sleep. Snoozers facing straight ahead are probably just resting their eyes and will therefore be most likely to get off soon.

Stand next to their seat, but not directly in front, leaving a passage for them to get to the door and for you to block seat predators from the reverse angle. Conversely, people sleeping with faces turned upwards — especially with their mouths open — should be avoided as they will almost certainly still be in their seats by the end of the line. It is also important to eavesdrop on mobile phone conversations for remarks like “I’ll be there in five minutes”.

While close human observation is vital, Mr Yorozu insists that “the mastery of the art of sitting down means first mastering the art of queueing”. Japanese stations mark out the positions of the train doors on the platforms and formal queues for trains are the norm. Resist the temptation to head for the edges, he says. Stick to the centre of the queue as that will give you more room for manoeuvre inside the carriage and increase seat-probability by about 30 per cent.

Mr Yorozu’s final advice is to take notes on fellow commuters. “Passenger memo cards” are helpfully included with the book.

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