LONDON, April 26 (UPI) -- Two major British tobacco companies are under investigation for price-fixing, and 11 store chains are involved in the probe, the Office of Fair Trading said.

The tobacco companies are Imperial Tobacco, which makes Embassy cigarettes and other brands, and Gallahers, which owns Benson & Hedges and Silk Cut, The Daily Mail reported. The stores include major chains like Sainsbury and Tesco.

Cigarette prices rose more than 12 percent, about double the rate of inflation, during the period under investigation from 2000 to 2003.

The OFT said the companies gave price information to retailers that allowed cigarette prices to remain the same at different types of outlets.

The anti-smoking group ASH supports the investigation. ASH wants cigarette prices to be increased through taxes that would then go to the National Health Service.