The Mills Group has become the first convenience chain in the UK to introduce a 'Think 30' ID scheme.
Managing director Nigel Mills told C-Store the company had looked at a Challenge 25 policy, but decided Think 30 would remove the element of guesswork completely.
"Staff know that if they don't ask they are culpable," he said. "The policy tells staff and customers that underage sales is a serious issue and we have to tackle it. We have introduced a series of test purchases with overage purchasers, and have treated failure of internal tests as a disciplinary matter. The staff have responded well to the challenge."
Mills added that after a short-term drop in sales, customers had started to come back. "They are taking a positive view of what our stores are doing in their community," he said.
Local police have also praised the initiative.