The Walkers Rainy Days campaign, where consumers could win £10 if they correctly predicted where and when in the country it would rain, has been slammed by the Advertising Standards Authority after its terms and conditions were changed mid-promotion.

Walkers Snack Foods announced the campaign and invited consumers to register before it went live: at that point, the T&Cs said consumers could enter twice a day. But before consumers could actually start entering, Walkers changed the rules to limit entries to one a day.

The ASA received a complaint from a consumer who had stocked up on enough packets of crisps to enter the promotion twice a day, in advance of its going live. The consumer argued that the change in T&Cs meant the promotion had not been conducted fairly.

Walkers said that it had based its decision to allow two entries per household on response levels to previous promotions it had run, but that consumer engagement in the first stages of the promotion indicated demand would far exceed estimated levels.

As the supply of available map grid spots was limited by the availability of Met Office data, Walkers decided to reduce the number of plays to once per day to allow the maximum number of consumers the chance to participate.

It claimed this change to the terms and conditions was widely communicated to all the customers who had pre-registered, either via email or through the Walkers Facebook page.

Walkers believed that it had conducted the promotion fairly and did not believe that the change to the terms and conditions undermined the integrity of the promotion.

However, the ASA upheld the complaint. Its investigation found that 40,000 people had registered to play before the conditions were changed, and ruled that these people “would expect to be able to purchase and bank codes in accordance with the original conditions, and would be disappointed to find that their opportunity to participate in the promotion was reduced after the conditions were changed.”

The ASA said “it was not acceptable for Walkers to alter the terms and conditions of play during the competition, because to do so could cause unnecessary disappointment to participants.” It ruled that the promotion had not been administered fairly, and that it must not appear again in its current form.