Almost half of the premises targeted in a crackdown on underage drinking in Oxford served beer to a 14-year-old girl in undercover police checks.

Last Friday night, police sent the girl and a 16-year-old boy into nine pubs and off-licences in the city - four of which sold them alcohol.

Acting as a couple, the teenagers bought two bottles of beer at the Turl, in Turl Street; two cans of lager at Folly Bridge Store; four cans of lager at Supa Sava, in Botley Road; and a bottle of lager at Londis, in Walton Street.

Tony Cope, the police's Oxfordshire licensing co-ordinator, said this was the beginning of a renewed campaign to cut sales of alcohol to underage children, with up to three covert checks a month in the city.

And it has emerged three other premises in the county are on final warnings, having failed checks on not selling alcohol to under-18s.

Mr Cope said: "There are 790 licensed premises in the city area and we have just touched the tip of the iceberg, with nine tests and four failures, so there's a lot more work to be done.

"I think what we will see across the board is the initial failure rate, then the message gets across to everybody. It's not a general rule that four out of nine premises in Oxford are serving alcohol to under-18s.

"We have limited resources, so we're going to premises we feel may have a problem first."

Mr Cope refuted suggestions that the children were being used to trap licensees.

He said: "We're not seeking to remove anybody's licence because we want to. We just want to stop this underage drinking problem.

"I can categorically say the 14-year-old did not look anywhere near 18. We definitely do not use youths who look 18."

At present, 38 licensed premises are under investigation by police or councils in Oxfordshire. Over the past year, 31 fines and at least 18 written warnings were issued.

The Cotswold Arms pub in Burford; the Chequers pub, in Chipping Norton; and the Tesco Express shop in Cockcroft Road, Didcot, are on final warnings after failing checks twice.

Unless it appeals, the McColl's shop in Millbrook Square, Grove, will today begin a two-week ban from selling alcohol, after staff repeatedly failed checks.

Chris Jones, manager of the Cotswold Arms, said: "The problem isn't with teenagers drinking in pubs. It's when they get someone else to buy it and sit around in parks."

John Cooper, landlord of the Chequers, said on both occasions the bar was busy and the test purchaser was served by new staff.

He added: "I think it's very underhand and deceitful. We get tarnished with the reputation of serving alcohol to children and there's nothing further from the truth."

The manager of the Londis shop, in Walton Street, Oxford, who refused to be named, said: "The lady looked 18. People can get very offensive when you ask them if they're 18."

Abdul Rouf, owner of Folly Bridge Store, said: "I wasn't here but the person who served him said the bloke was very large and he thought he looked 21."

No-one at Supa Sava or the Turl pub was available for comment.