The headquarters of Britain’s biggest four supermarkets have been raided by the consumer watchdog as part of an investigation into price-fixing.

Tesco, Sainsbury’s, Asda and Morrisons are among those suspected of colluding to fix the prices of groceries and health and beauty products, in what is believed to be the biggest inquiry in the history of the Office of Fair Trading (OFT).

Almost 100 investigators and lawyers are understood to have seized hundreds of e-mails between the retailers and their suppliers during the surprise raids on Thursday.

Firms found guilty of price collusion can expect punitive fines under the Competition Act, equivalent to 10% of the sales turnover of the product involved.

News of the raids comes two days after the OFT announced it was looking into allegations of collusion over the price of cigarettes.

The major four supermarkets are among 11 retailers caught in the cigarettes inquiry, which is said to involve Imperial Tobacco, maker of brands such as Embassy, and Gallaher, which owns Silk Cut.

The watchdog had already been investigating price-fixing claims against Morrisons and Tesco regarding milk, butter and cheese. Sainsbury’s, Asda and several dairy firms had already admitted collusion and been fined.

Last week the OFT was forced to pay Morrisons £100,000 for naming it as one of the firms under investigation before publication of the official report.

A spokesman for Tesco said last night: “We are surprised by these allegations of collusion. Tesco’s record on achieving the lowest prices for customers in a ferociously competitive market is clear.”

The OFT declined to comment. It has recently been criticised by business leaders for conducting investigations of the construction, banking and retail industries in the public spotlight. This week the Competition Commission will publish the results of a two-year review of the groceries market.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive