A bar owner shut his customers in and called the police after suspecting most of them were underage.

Ronny Carter said he took the drastic action at Oxford's G-Bar on Friday night to strike back against under 18s going into pubs and clubs.

Each of the 23 people in the downstairs bar had produced apparently authentic identification - such as a driving licence, student card or birth certificate - on the door to prove they were 18 or over.

However, after consulting staff at 8.30pm at the bar in Penny Farthing Lane, Mr Carter suspected the IDs might be fake. So he turned the lights on and told those in the bar the police were on their way to check their IDs.

Officers arrived within 15 minutes and when a Pc told anyone who was carrying fake IDs to sit down, only one person remained standing, he said.

Mr Carter said police agreed there was no way to differentiate between the fake and the real IDs.

He said: "It is ridiculous. As a responsible bar owner what am I up against? They buy them on the Internet and they are perfect copies.

"I want to send a clear message to any youngsters that try to get in that we won't tolerate it. Sometimes people look 18 and if they have got ID to back it up it is very difficult for the door staff. Unless we have got access to a national database it's almost impossible."

Mr Carter admitted it was a big gamble, but said he was glad he took the action.

"They spend up to £100 an hour, but I want to get across to these kids that it is us that gets the fine and could go to prison.

"It is nothing we have not all done when we were young. The problem is if one of them gets injured here, they are going to have real problems with insurance.

"Also they are very young and there are all the problems related to that, like being sick.

"This is what they do not understand, they think we are just giving them a hard time."

The fake IDs were seized and those using them were given a warning by police.

Thames Valley Police spokesman Adam Fisher said: "Any youths who are found drinking alcohol underage can be arrested and we would ask parents to be aware of what their children are up to in the evenings or they could get a knock on the door informing them their son is in custody.

"We support the action that Mr Carter took in trying to tackle the problem of underage drinking and if other landlords have similar concerns they should take the same action and contact the police."

Oxford's Nightsafe, the scheme to combat the city's drug and alcohol-related problems, has been targeting underage drinking.

In February, staff at four premises were fined for serving two 15-year-old girls.