The deal, which includes a broad range of products from cheese to muesli, is being advertised on TV and press and flagged up on the homepage of Aldi's website. It represents about 15% of Aldi's SKUs.
Paul Foley, MD of Aldi in the UK and Ireland, said the prices were not a special offer and would be held indefinitely as part of Aldi's commitment to everyday low prices. Some of the prices had been dropped to 99p "to help consumers", but the majority of the products being flagged up were 99p before the pricing initiative was brought in.
"99p is our most common price point and we thought we would point that out to consumers," said Foley. "We noticed that if we did a comparison of all our 99p products we were up to 30% cheaper than our competitors and thought we should highlight that. Most £1 deals in other stores are short term promotions - ours are everyday low prices."
Aldi claims the number of shoppers using its stores is 11% up in the first three months of 2009 compared with the same period the previous year.
Over the past six months, it has seen a trend of customers moving "from top-up to fill-up shopping" in its stores, with the size of a typical Aldi basket increasing by about a third.
"Avoiding short-term promotions offering consumers freebies and multiple-products they don't need enables our customers to save more at the check-out," added Foley.
"This is causing more shoppers to step out of their supermarket comfort zone as they aim to save money while maintaining their quality of lifestyle."
TNS data for the 12 weeks ending 19 April show Aldi's sales were up 13.6% compared with the same period the previous year, giving it a 2.9% share of the market.