Northamptonshire County Council Trading Standards says it will take action against shopkeepers found to be selling tobacco to underage customers.
The warning follows a series of test purchases by Trading Standards in which a 16-year-old attempted to buy cigarettes from shops in Kettering and Wellingborough.
Of the 11 test purchases, the underage customer was able to buy cigarettes without having proof of age on two occasions.
The test purchases were carried out last month after a number of complaints to Trading Standards and based on intelligence received about the shops.
Proof of age
Businesses are now being reminded that they must ensure they do not sell to under 18s. Most businesses do this by operating a Challenge 21 or Challenge 25 policy. If a customer looks under that age, proof of age is required, and staff must be trained to verify age before selling age-restricted products.
Businesses found to be selling cigarettes to any person under the age of 18 could face a fine of up to £2,500.
A series of test purchases of e-cigarettes have also been made at supermarkets, specialist e-cigarette shops, market stalls, independent newsagents and local convenience stores by Trading Standards over the past 12 months.
Of the 40 premises visited, test purchasers were able to buy e-cigarettes – which must not be sold to under 18s - on 19 occasions.
County council cabinet member for public protection, strategic infrastructure and economic growth Cllr André Gonzalez de Savage said: "While it is reassuring that the majority of businesses selling age-restricted products are abiding by the law and helping to keep children safe, there are still shopkeepers who are not checking proof of age.
"Simply asking a customer how old they are is not enough, sellers must ask for official proof of age before selling tobacco and other age-restricted products.
"Our Trading Standards team will continue to carry out checks and test purchases whenever we receive complaints and intelligence about underage sales."
Members of the public who have information about the sale of age restricted products to children should call Citizens Advice on 03454 040506 or visit the citizens advice website.
Any business that would like further advice can go to the Northamptonshire Trading Standards website.