Nearly a quarter of shops tested by a tradings standards 'drink squad' were caught selling alcohol to under-18s, an Oxfordshire County Council survey shows.
Test purchases were carried out at 66 shops in the county, with 15 failing to observe under-age drinking laws.
Police, working closely with trading standards officers, issued £80 fixed penalty fines to offenders.
The figures were revealed as a hotline set up in north Oxfordshire to prevent young people becoming hooked on booze was relaunched.
And the county council is renewing an appeal for people to report shops that sell alcohol to under-18s.
Richard Webb, group manager of Oxfordshire Trading Standards, said the 22 per cent figure reflected national statistics.
He said: "Our survey was done between April 2005 and April 2006, and it is ongoing.
"I am disappointed at the number of shops selling alcohol to under-18s because we put a lot of work into advising and assisting businesses.
"Prosecutions are difficult, but we work closely with the police who come with us when we carry out test purchases. They issue fixed penalties to offending stores. Seven fixed penalties have been issued since April this year."
Oxfordshire's trading standards team recently launched an Anyone for a Drink' campaign in partnership with Cherwell District Council and Thames Valley Police, with a hotline on which members of the public could report law-breaking shops.
Only seven people called the number in two months, and the campaign has been relaunched with a new appeal for people to name shops selling alcohol to under-18s.
Dr Kelechi Nnoaham, public health registrar with Oxfordshire Primary Care Trust, said: "Under-age drinking has consequences for health services and the individuals concerned.
"Hospital admissions of children with acute alcohol poisoning have dramatically risen (10-fold increase in the last 10 years) with obvious impacts on stretched health services.
"The sexual health of teenagers is also affected by alcohol use, with 75 per cent of under-20s using contraception when sober, but only 13 per cent taking precautions when drunk."
Barry Wood, leader of Cherwell District Council, said: "We are committed to finding new ways of stopping alcohol being sold to anyone under 18."
Ray Jelf, county cabinet member for community safety, said: "Trading standards are continuing to fight the illegal sale of alcohol, and any information that would help us should be reported."
The anonymous hotline is on 01865 815500.
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