There is a strong police presence in Builth Wells during the show

In partnership with Powys Council's trading standards department, officers are sending young people into pubs to pose as illegal drinkers.

Last year, one senior officer described the young people's village at the show as "Ibiza without the sand or sea".

The Royal Welsh Agricultural Society said excessive drinking could result in people being ejected from the show.

The show attracts more than 200,000 people every year to its mid Wales home of Llanelwedd, near Builth Wells, and last year some 12,000 visited the young people's village over the four days.

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The village has its own bars and live music acts entertain the young people.

Chief Inspector Steve Hughson said the exercise involving children would be "strictly controlled".

"We are engaging with trading standards to help prevent alcohol being sold to underage people," he said.

"We have some young people aged 14 and 15 asking for beer in pubs".

He added the young people taking part were not allowed to dress to look older than they were.

Chief Insp Hughson said: "This will be strictly controlled and if we identify people selling alcohol to underage people then we will consider taking action."

He added that excessive drinking among young people whether at the show or not was "always a concern" to officers.

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"We are working with Powys Drug and Alcohol Centre which will have outreach workers at the show advising people about substance misuse, including alcohol. It's a very pro-active approach," he said.

"We will also be issuing fixed penalty notices for minor public order offences and anti-social behaviour. A fixed penalty will cost �80."

The Royal Welsh Agricultural Society said excessive drinking could result in people being ejected.

The society said: "It will be an offence to carry alcoholic drink around the showground.

"Drinking in public places, especially in the avenues, will be an evictable offence and members will run the additional risk of having their membership cancelled. "

Arrests

Last year, Dyfed-Powys Police's Inspector Geraint Rees described the young people's "village" at the show as "Ibiza without the sand or sea".

He said police wanted to meet show organisers, licensees and others to crack down, although he said those who drank too much were in the minority.

But the Young Farmers' Clubs in Wales said they worked closely with the authorities to make the event safe.