The consumer watchdog has warned that some shops are failing to clearly display prices.
The Competition and Markets Authority says this could prevent shoppers from comparing prices.
However, he said the evidence suggests that historically high food price inflation has not been due to weak retail competition.
The CMA has written to shops that are failing to clarify prices – and warned them to make the necessary changes or face enforcement action.
It has also asked the government to reform pricing legislation to help shoppers find the best deals.