Potentially lethal “laughing gas” with a street value of about £6,500 was seized in just one night by police outside the pubs and clubs of Shoreditch.

More than 1,200 canisters of the “legal high” chemical nitrous oxide were taken off nine unauthorised street sellers in the joint police and council operation on Saturday July 19.

The canisters are used to fill balloons which are then sold for up to £5 to users who inhale the gas for a short rush.

The substance starves the brain of oxygen, making users light-headed and disoriented for a few minutes.

Occasionally it can kill, by displacing oxygen from the body.

Earlier this month a Londoner drowned after inhaling the gas at a festival in France before going for a swim.

In February a 21-year-old chef died after inhaling nitrous oxide shortly after hearing he was to become a father.

In 2012, a 17-year-old student from north London died after suffering a heart attack and brain damage after inhaling what was being sold as ‘laughing gas’, but which actually contained other lethal gases.

Home Office figures showing 350,000 16-24 year olds used nitrous oxide last year have increased concerns over its growing popularity.

Inhaling nitrous oxide is not illegal, however Hackney Council is combating its sale by using Section 38 of the London Local Authorities Act 1990, which allows local authorities to enforce against unauthorised street trading.

Acting Chief Insp of all Neighbourhood policing in Hackney, Ian Simpkins, said: “They’re not illegal per se but it is illegal to sell them on the street and the council deal with that aspect.

“The main problem is the litter and noise associated with them, and the fact it’s quite profitable means it attracts organised gangs who will ‘defend their patch’.

He added: “The small canisters are legitimately used for whipped cream refills and in medicine, but they can also fill balloons which are then sold and inhaled.”

Cllr Feryal Demirci, the council’s cabinet member for neighbourhoods, said: “This so-called legal high can be extremely dangerous - not only does it put people at risk, it promotes anti-social behaviour.

“The empty balloons and nitrous oxide canisters also create a lot of litter in Shoreditch and Dalston, which is frustrating for residents, local traders and shoppers. It also costs taxpayers’ money to clean up.

“We want to send a message out to the thoughtless peddlers of this dangerous gas – they’re not welcome on the streets of Hackney and we will take action to remove them.”

The nine offenders will be fined £150 for unauthorised street trading and several will also be fined £80 for littering.

One trader, who police had previously seen selling nitrous oxide, will be prosecuted and could face a fine of £1,000.