A Walkers crisps promotion for free film rental and cinema tickets has been given the go-ahead, after complaints that larger packs had a greater chance of winning than smaller packs.

Consumers guess the movie title from the clue on the card inside Doritos packets and have the chance of winning either a free Blockbuster movie rental or ODEON cinema ticket.

The complainants challenged the promotion’s claim “one in four packs on average contains a “Free Movie” gamecard. They believed that larger packs had a greater chance of winning than smaller packs.

However, the Advertising Standards Authority said the gamecards were inserted automatically using a computer system linked directly to the bag maker and the cards were distributed equally between all sized packets. They explained that there were daily checks to ensure that the correct ratio of gamecards was achieved.