Forget crosswords. Britons now like their puzzles with numbers.

Some Britons have been a little distracted of late. Pen in hand, brow furrowed, Hazel Warren has been so engrossed that she forgot to put the dinner on. Others have been late to pick up the kids from school, feed the dog, or start the day.

The culprit? A simple Japanese numbers puzzle called Sudoku that is gripping Britain. Newspapers have fallen over each other to feature it. National championships are promised. A Sudoku book has become an instant bestseller. Logic has not been this fashionable since the Rubik's Cube.

"They took over my life," says Ms. Warren of Rochdale, northwest England. "Since I also have a job, I had to really restrict myself to only doing the Saturday one.

"The beauty of Sudoku is its simplicity while at the same time challenging one's powers of logical thinking," she adds.

Sudoku, which means "single number" in Japanese, is essentially a simple logic problem with layers of hidden complexity that can draw the solver in to the point of obsession. A grid nine squares by nine is presented in which all the integers from 1 to 9 must appear in every row, every column and every 3-by-3 box. So far, so good.

Some numbers are given as initial clues. Then, by process of deduction, sometimes resorting to quite intense logical assumptions, the solver can slowly begin to work out what goes where.

"It's the sort of puzzle that you can do everywhere," enthuses Michael Mepham, who sets puzzles for The Daily Telegraph. Since he started out in February, he has received tens of thousands of e-mails and his website has attracted more than 250,000 hits.

"I get so many e-mails from people who've missed their stop on the tube or gone to the wrong station on the train; people who forget to feed the dog or pick up the kids from school," he says.

Yet a few months ago, few here had heard of Sudoku. The idea, which traces its origins back to the 18th-century noodlings of a Swiss mathematician, has been popular for years in Japan, where linguistic complications make word-based puzzles like crosswords less viable.

It was spotted by a retired Hong Kong judge, Wayne Gould, who wrote a program to create the grids and began to peddle them to newspapers. The Times (of London) was the first to see the potential. Others rapidly followed suit.

Part of Sudoku's current popularity is undoubtedly due to the way newspapers have hyped it. Gimmicks are important to the British press. Tabloids have fought bitter wars in the past over trivial features such as bingo. In a perennially declining market, a new fad is a valuable commodity.

"It definitely makes a difference to circulation," says Michael Harvey, features editor at The Times who helped commission England's first Sudoku puzzles. "It draws readers into the paper. Anecdotally we've had lots of people saying they have been drawn to The Times."

Some featured more than one a day. Sudoku snobbery set in, with all claiming theirs were the best puzzles. The Times offered a cellphone download version. The Independent and the Times are both organizing national championships. The Guardian, tongue in cheek, put a puzzle on every page of its feature supplement and said they were the only ones handwritten on the slopes of Mount Fuji.

But is it any good for you? If claims can be made that video games and television make us smarter, must not Sudoku have some benefits as well? Or are rather a lot of people wasting rather a lot of time?

Trevor Hawkes, a mathematician, says it's a good cerebral workout, and could be particularly useful for children. (His 12-year-old is a big fan.)

"In a nutshell it's good mental exercise, particularly for teaching children to work out strategies for problems they've not seen before," Mr. Hawkes says. But it doesn't spell disaster for the British crossword, suddenly sidelined by this new trend.

"Cryptic crosswords are fascinating, too, and good for verbal skills, mental associations, and general knowledge - a different kind of knowledge than needed to do Sudoku," says Hawkes. "Neither is better than the other.... They complement each other."

Sudoku puzzles can vary in difficulty, depending on the number, type, and positioning of clues. Some lead the solver more or less directly through to the solution (and for the sake of purity, there should be only one possible solution). Others require more complex logic strategies to steer a way through the numerical soup.

Thus more committed fans will engage you in subtleties of bifurcation and Ariadne threads, of trial and error versus pure logic.

Woe betide if you make a mistake. John McLeod, an afficionado from Wimbledon, says it's a miserable moment when you realize you have duplicate numbers.

"There's no unpicking it," he warns. "You have to go right back to the beginning. You won't remember the order you've done things and so there's no alternative other than to go back.

"For me, the thrill of Sudoku is getting to the last bend and seeing if it's all going to go through or have I made a mistake. For me, it's a question of traveling hopefully rather than arriving."