This retailer's profits have gone nuts - thanks to adult colouring-in books

UK stationary retailer WHSmith announced an 11% jump in pre-tax profits to £80 million ($114 million) for the six months to February on Wednesday - thanks in part to strong sales in "adult activity books, such as colour therapy, extreme dot-to-dot and querkles."

Like-for-like stationary sales increased 5% because of adult activity books, especially since the chain opted to market them at the front of the stores.

This trading update isn't the first time WHSmith has cited an increase in the sale of colouring-in books for stressed out adults as a reason for overall growth. At Christmas, the company said its strong performance over the period was "driven by the 'colour therapy' phenomenon."

Grown-up colouring books have now grown so much in popularity that Amazon, the online retailer, has an entire shopping category devoted to adult colouring books, where you can buy colouring books like a London A-Z map or one of actor Benedict Cumberbatch's face.

Along with strong colouring book sales, WHSmith CEO Stephen Clarke said in the report that the retailer's expansion into airports and train stations is paying off.

"The Travel performance reflects our ongoing investment in the UK business and growing passenger numbers while internationally we have now secured over 200 stores, including our first airport shops in Spain and Germany" Clarke said.

While the company reported strong profit growth in the six months to February, sales in its high street stores were flat. That news seems to have spooked investors on Wednesday morning, and just after 10:30 a.m. BST (5:30 a.m. ET) shares are down more than 3%. Here's how that looks: