Supermarket chains are failing to clamp down on underage knife sales despite pledges to improve staff training.

Test-purchasing specialist Serve Legal saw the number of supermarket staff asking 18 and 19-year-old testers for ID drop to 76% for the nine months to the end of March. This was down from 78% during the previous five months.

Serve Legal warned supermarkets they could face an increase in prosecutions as authorities have given every indication that they plan to step up stings. However, the pass rate for knives is better than for other age-related products, with a 70% pass rate for sales of alcohol and 66% for cigarettes.

"Retailers take this seriously," said BRC spokesman Richard Dodd. "They are actively engaged with the Home Office to reduce and eliminate knife sales to young people."