The group, which includes members of the Wine and Spirit Trade Association, British Retail Consortium and the Association of Convenience Stores, has introduced new signage to help enforce the control, which it believes will help reduce proxy purchases as well attempts to buy alcohol underage.
RASG chairman Nick Grant said that Challenge 21 had been an effective tool, but now was the time to raise the bar. "Retailers have done much to reduce levels of underage purchase, but it's time to go a stage further," he said.
"Feedback from frontline staff suggests they want the freedom to challenge more widely to ensure young people are not breaking the law. Challenge 25 makes this a reality."
Simon O'Brien of the Association of Chief Police Officers said: "This is a sign of determination from those involved in the sale of alcohol to work towards the goals of safe and sensible alcohol consumption."