THE archetypal family board game Scrabble already has a legacy to rival that of a small European nation. At least 150 million sets have been produced in more than 120 countries, along with a list of some 276,000 'legal' words. And more than half of UK homes have Scrabble on their shelves, while roughly 30,000 games are started every hour.

It might be surprising that such a geeky a game has inspired such a devoted following, but perhaps the secret to Scrabble's success lies in accessibility. The aim of the game is simple – use letters to make words and score points – and it epitomises that winning combination: straightforward to learn, complex to master.

It's fair to say that Scrabble is looking pretty good at 70. It's not so much that the game hasn't aged during that time – more that it's barely changed at all. Barring the unheralded Scrabble Trickster, the rules have remained almost identical since incorporation in 1948, while 'new editions' tend to limit themselves to slightly swanking up the board.

Even comparable classics like Monopoly have made some token innovations (see glorious misfires like FedEx Monopoly, Bass Fishing Monopoly, and an edition based on The Powerpuff Girls), but for Scrabble, the old ways have always been the best.

As with so many iconic American inventions, the early days of Scrabble follow a classic narrative of failure, perseverance, and the 'American dream'. In the early 1930s, Alfred Mosher Butts was an underemployed New York architect, struggling beneath the weight of the Great Depression. After an equally unsuccessful stint as a painter, Butts decided to take two popular pastimes of the day – crosswords and anagrams – and combine them into a single game. He determined the frequency of different letters by analysing hundreds of copies of The New York Times, The New York Herald Tribune, and The Saturday Evening Post.

His resulting creation, Lexiko, met with rejected patents and slammed doors, while a regrettable rebrand as Criss-Cross Words fared little better. But just as Butts began to lose hope, a lifeline arrived in the shape of James Brunot, an entrepreneur and avowed game-player, who renamed the project Scrabble and pushed it into commercial production.

The game was picked up by Macy's, and sets were soon flying off the shelves of the very same companies that had previously rejected it. Butts lived off the royalties for the rest of his life.

Scrabble was seemingly the perfect product, and it spent the subsequent decades smoothly outselling its competitors with little or no alterations. As the game's global reach grew, so too did the potential for international competitions. 1991 saw the first Scrabble World Championship – though the London-based event was nearly cancelled after all the participants assumed someone else would bring the tiles.

The 2016 Scrabble World Champion Brett Smitheram has been a Scrabble Grand Master for more than 20 years, and knows better than anyone how intensely the game can be played. "I would classify it as a 'mind sport'," he says. "Certainly, it ceases to be a game – we're playing it at a much higher level – and a lot of aspects of sport do carry over. When I won my World Championship, I was at my physical peak, and physical ability plays directly into your ability to concentrate."

Scrabble mastery is a mixture of memory, temperament, and analytical skill, but the exertions of the game have not always found universal recognition. Journalists often challenge Brett to games during interviews, and are disappointed when they inevitably lose. "You wouldn't expect to beat Mo Farah at a marathon," he points out.

The Scrabble community guard the game with zealous enthusiasm. New additions to the lexicon can cause major controversy (this year 'twerk' was the primary eyebrow-raiser).

Scrabble may be famously family-friendly, but it can also cause the kind of domestic dust-ups normally reserved for politics and religion. In 1996, a woman from Maryland was charged with assault after whacking her husband over the head with a Scrabble board and a five-year-old from Leicester once phoned the police when he suspected his sister of cheating.

"If you lose at chess, you've just lost a couple of pieces on a board," explains Brett, "but losing at Scrabble brings into question your ability with your own language. People take it as an indictment."

So, at 70 years of age, this word game of word games is doing just fine, and in 2019 devotees can look forward to another programme of tile-tapping Scrabble extravaganzas. (You should write that one down. It's worth 33 points.)

One final Scrabble fact for you: It is estimated that there are over a million 'lost' Scrabble tiles floating around, many of them erroneously eaten by dogs.