A nightclub is being investigated after illegally selling laughing gas to revellers.

The Ocean Rooms in Brighton provided a dedicated "gas room" where ravers would queue up for hits of nitrous oxide.

Clubbers would buy balloons full of the gas for £2 before inhaling it with their friends. They then experienced a rapid but short-lived high.

But police, together with Brighton and Hove City Council, have begun an investigation into the use of the gas, also known as "hippy crack", at the club in Morley Street.

Nitrous oxide is an anaesthetic commonly used for dental patients and women in labour.

It is illegal for anyone but a registered pharmacist, at a pharmacy, to sell or supply it for inhalation.

Licences belonging to clubs involved in selling the gas could be reviewed by the council. Supplying the gas illegally also carries a possible two year prison sentence.

Trevor Madison, production manager at the Concorde 2 said it had also been approached to sell the gas last year but decided against it. He was, however, involved in running trance night Dirty Weekend at the Ocean Rooms where balloons of nitrous oxide were being sold.

He added: "We had no idea we were breaking the law. If I had we'd never have done it. We looked at what other clubs were doing - looked on YouTube and MySpace - and there's loads of places doing it."

Experts believe the gas has proved popular because users perceive it to be safe and legal. It causes a "rush"

by starving oxygen to the brain - which can lead to users collapsing.

The Medicines and Healthcare Products Regulatory Agency (MHRA) has warned regular use of the gas can cause lasting damage. It said it would investigate the club.

Danny Lee Frost, head of criminal investigations at the MHRA, said: "It suppresses the bone marrow. It causes hypoxia which drives oxygen out of the body. And there is some suggestion that it can cause brain damage."

Last year Daniel Watts, a 23-yearold company director in the West Midlands, suffocated while taking laughing gas.

But Mr Madison said: "It's not addictive. It only lasts a few seconds.

It's no different from having a strong shot, something like Absinthe, from the bar."

Ben Gill, manager of The Ocean Rooms, told Sky News neither he nor party organisers were aware they couldn't sell it to clubbers.

He added: "No one is aware of any laws being broken. It is really widespread.

"A lot of nightclubs are doing it and it is at nearly every festival."

A spokeswoman for Brighton and Hove City Council said: "This practice is dangerous and illegal and officers will be visiting premises and sending out letters to make sure that all club owners know that under no circumstances should they allow the use of N2O on their premises.

"Officers are considering a possible licence review for any clubs found to be involved."