Price competition from pound shops is here to stay and grocers ignore the mounting threat at their peril, new research from YouGov suggests.

The Rise and Rise of the Pound Store Phenomenon argues that the single-price discounters have changed consumer behaviour for ever. Even if the economic crisis ended tomorrow, consumers would not revert to buying everything from the supermarkets, YouGov consulting director Rob Cushen said.

"People used to pay a premium for the convenience of a supermarket but they traded that for cheapness," he said. "They aren't going back. They will still shop at the supermarket, but will get certain items more cheaply at the pound store."

Almost a third (32%) of shoppers visit a pound store once a month. They are most likely to buy cleaning products, toiletries, chocolates, sweets and snacks, the survey revealed. "The situation is not static," Cushen added. "Supermarkets must respond to defend their territory [from expanding pound shops] or they could suffer a gradual erosion."

But the mults dismissed the threat. "Our Essential range has brought us a bigger market share and we don't see pound shops as competition in this area," said a spokeswoman for Waitrose.