Sixteen months ago The Times took a gamble on a new puzzle that had turned up unannounced in Wapping under the arm of a man who wondered if it might prove an “absorbing time-filler” for readers. That man was Wayne Gould, and his logic puzzle, Su Doku, has not only enslaved the nation’s commuters but is now being hailed by teachers, doctors, scientists and even the Army as the ultimate brain workout.

The impact of Su Doku has been unexpected, to put it mildly. The first e-mail in what was to become a mountain of correspondence on the subject arrived at The Times on the first day of publication: “Sir, Su Doku puzzles should carry a warning. It’s only Day 1 and already I’ve missed my Tube stop. Yours truly, Ian Payn, Brentford.”

Today 336 Su Doku books are available globally. The six bestselling titles in the UK sold 1.7 million copies last year. Sudoku Magazine (one of many) sells in 32 countries; 402,000 copies were sold in Britain in the second half of last year. Su Doku is even taking over our TV screens: BBC One’s Sudo-Q with Eamonn Holmes (1.6 million viewers), ITV2’s Play Sudoku (from 1.30am nightly), Channel 4’s daily Teletext Su Doku and UKTV’s Street Cred Sudoku. Hugh Laurie’s character in the US TV series House, MD played online Su Doku in an episode in December (Su Doku has reportedly now been banned from the set to cure the cast’s addiction). Should you tire of the pencil and paper format, you can now have Su Doku beamed to your mobile phone, play the board game, log on to a range of websites, buy an electronic Sudoku Master Puzzle handset, purchase the playing cards or, on a dull afternoon, slip Carol Vorderman’s Sudoku CD-Rom into your PC. A Nintendo version for DS is due out in May.

So far, so trivial. But for those with a professional interest in mental agility and logic, Su Doku has the potential to be more than a mere pastime. Studies at Trinity College, Dublin, and the Rush Alzheimer’s Disease Centre in Chicago have shown that doing Su Doku and other mental exercises such as crosswords keeps the brain sharp into old age and is likely to lower the risk of Alzheimer’s. The Times journalist Damian Whitworth discovered last month that extreme Su Doku is now a crucial part of officer training in the British Army.

It is now widely used in schools to encourage analytical and lateral thinking, and has been endorsed by the government-sponsored Teachers magazine. The mathematician Sir Michael Atiyah has declared it to be “a good thing” for schoolchildren, and two sessions of the Mathematical Association’s annual conference next month are devoted to the puzzle.

Teachers attest to Su Doku’s popularity with children, both for work and play. Chris Harrison, the head teacher of Oulton Broad Primary School in Suffolk, started photocopying puzzles from newspapers to show to a few pupils, but they proved so popular that he bought a Su Doku whiteboard to put up the playground. He says: “It goes up for morning break. We normally have about half a dozen children gathered round the board — it’s a collaborative process, so there’s a bit of give and take.”

He says that as well as being enjoyable, Su Doku has educational benefits. “We try to raise awareness of maths in all sorts of ways; this is just one way we do it.”

Gill Dillon, a maths teacher at Abraham Guest High School in Wigan, introduced it early last year. “I started using them with a group that I felt had more ability than they were letting on,” she says. “There was a bit of reluctance at first, but then they really started to engage with it.”

The most beneficial aspect is that it teaches children about problem-solving: “You need to be able to hold different pieces of information in your head, and set out a strategy. Sometimes children’s biggest problem with maths is a lack of confidence; knowing that they can solve Su Doku gives them that confidence.”

One school even harnessed the popularity of Su Doku to raise money. From Monday, pupils at Neston High School in Cheshire will be taking part in a fortnight-long sponsored Su Doku-thon, to raise money for computer equipment. All the school’s 1,600 pupils will spend one of their maths lessons doing as many Su Doku puzzles as they can. Fiona Matthews, the secretary of the school’s Parents’ Forum, says: “It can be hard to get teachers involved in fundraising because they are so busy, but this has gone down really well. It’s interesting, unusual and appropriate.”

Su Doku has conquered Europe, North America and Australasia, spread across much of South America and Asia and has footholds in Africa. It is now truly global.

The writer P. D. James has suggested that puzzles are popular because they fulfil a fundamental craving for “restoration of order”. If we can find an internal logic at the heart of things, it makes us feel more in control of external chaos. Whatever the deep-seated cause, if Su Doku really can make double maths lessons exciting, it’s nothing short of a miracle.