The city council's trading standards service sent in youngsters aged from 13 to 15 to try to buy cigarettes, alcohol and age-controlled videos in outlets.

More than 50 retailers in the city were "tested", with 17 failing.

Councillor Mike Carr said the week-long exercise showed some retailers were not complying with the law and would now "face the consequences".

Protect health

If the council prosecutes the shop owners, they face fines of between �1,000 and �5,000.

Mr Carr, cabinet member for personnel and direct services, said: "These age controls are essential to protect the health of young people and to help curb anti-social behaviour.

"Retailers should be well aware of these age restrictions and the products they apply to.

"Unfortunately, this exercise has shown that some retailers don't always comply with the law, and they will now have to face the consequences."