Retailers are being urged to do more to reduce under-age alcohol sales despite a significant reduction over the Christmas period.

Test purchasers visited more than 6,000 licensed stores during local authority Trading Standards’ six-week campaign, and were illegally sold alcohol in 20% of them - down from 36% last summer.

Association of Convenience Stores chief executive David Rae said it was satisfying that, in the largest test purchasing campaign conducted to date, there had been a significant improvement, but added that a 20% failure rate was still unacceptable.

He said: “Test purchasing is going to get tougher and Trading Standards and police in some areas are willing to change the rules to ensure more test purchasing failures.”

The Retail Alcohol Standard Group - a group of retailers set up to tackle the problem of sales of restricted goods to those underage - said it would now conduct a review to come up with best practice.

A spokeswoman said: “Some people managed better improvements than others and we want to work out how they did it.”

It has commissioned research to find out why sales are still being made to under-18s, despite large amounts of time and money spent on staff training. The group is also talking to Trading Standards authorities about incorporating its ‘Under 21?’ signs into their literature.

She added: “We want a cultural change so that young people are more prepared to carry ID and be more open about being asked - they often aren’t and can get aggressive, which is a real problem for retailers.”

Government figures show that violent crime fell by 11% during the Christmas clampdown on alcohol disorder, while serious violent crime fell by 21% over the same period.