99p Stores has laughed off a Watchdog investigation into the chain as “flawed, stupid and bad journalism” - and thanked it for a subsequent boost in sales.

Last week, the BBC show attempted to discredit price promises made by the discounter by comparing its prices with the big four’s.

However, co-founder and commercial director Hussein Lalani, who appeared on the show, claimed the report had backfired and that in the three days following the show, sales across the discounter’s 168 stores had leapt 22%.

“I would like to formally thank Ms Anne Robinson for this very welcome surge in business,” Lalani said.

The Watchdog report showed researchers buying a basket of 40 products from 99p Stores and finding that seven were cheaper at the big four.

“That was just clutch ing at straws,” said Lalani. “What they didn’t say was that all seven products were on offer at the time - otherwise we would have been cheaper on all of them. But seven products out of 40 means 82.5% of the time we are cheaper than supermarkets, even when they are running so many promotions.

“Our prices don’t change with seasons, whims or on the back of multi-million-pound TV advertising campaigns.”

Lalani said the highlight of the show was when he pulled a poster out of his pocket that stated: ‘Great News! 82.5% of products checked by Watchdog are cheaper in 99p Stores than your leading supermarket - and we’re working to bring you 100%.’ The posters are now up in all 99p Stores.

“When I pulled out the poster Anne Robinson’s face was a picture,” Lalani added. “I’ve now got that moment in time framed on my desk.”

99p Stores currently has 164 stores across the UK. It expects to hit 200 by the summer and open another 40 in 2013.