The Office of Fair Trading (OFT) has cracked down on the four major supermarkets, Tesco, Asda, Sainsbury's and Morrisons.
The Sunday Telegraph reported the regulator has raided the offices of the grocers in a new price-fixing probe that ranges across food and toiletries.
Several of the supermarkets confirmed the news, although Morrisons refused to comment on the reports.
A Tesco spokesperson said: "We understand that the OFT has asked for information from a wide range of suppliers and retailers. We are working with them to provide what they require.
"At Tesco we are confident that we always act in the interest of consumers. Indeed, over the last ten years we have saved the average family almost £5,000 as a result of our investment in price."
Health and beauty products have been targeted in the latest probe, with suppliers also included in the enquiry. Procter & Gamble also confirmed OFT officials visited last Thursday.
Last week, the watchdog said it was investigating several supermarkets over claims of fixing the price of tobacco, while the week before the OFT announced widespread evidence of bid rigging in the construction industry.
The watchdog has the power to fine companies found guilty of anti-competitive behaviour up to ten per cent of their turnover.
The OFT was also recently forced to apologise to Morrisons and pay the grocer £100,000 over a press release relating to yet another enquiry into allegations of dairy price fixing was found to defame the company.
The Competition Commission is currently looking into the supermarket industry in the UK, but has reported so far that the market is very competitive.