Food writer: 'Don't trust supermarkets to give a good deal'
30 November 2012 Last updated at 12:50 GMT
Eight supermarkets have agreed to ensure that special offers and price promotions are fair.
The Office of Fair Trading has been investigating the way prices are displayed, advertised and promoted in stores.
It raised concerns about prices being artificially inflated to make later discounts look more attractive.
Investigative food journalist Joanna Blythman said she believes supermarkets have been playing "fast and loose" with pricing practices for some time.
She advised shoppers to ''be sceptical''.