The mass inhalation of nitrous oxide was to protest against the Government’s plans to crack down on legal highs.
Some of the protesters erupted into giggles before spreading out across the lawn.
Figures suggest laughing gas is the fourth most used drug in the UK and that 400,000 used it in 2013-14.So-called laughing gas is the fourth most used drug in the UK.
Although conventionally used as an anaesthetic during dentistry and child birth and as an aid in the manufacture of whipped cream, the substance can be used as a mood enhancer.
The cause of death of a teenager that had been linked to laughing gas was last week deemed “inconclusive” after a post-mortem.
But the Government wants to include it in a bill that will make it illegal to sell any “psychoactive substances” other than alcohol, caffeine and nicotine.
It comes after several other deaths have been linked to so-called legal highs – drugs that produce a psychoactive response but are not currently classified under the UK’s drug rating system.
While possession will remain legal so long as there is no intent to supply, the bill could mean up to seven years in prison for people who provide drugs to others.
The director of the Psychedelic Society, which organised the laughing gas protest, says it is not the job of the Government to tell people what they can and cannot use.
Stephen Reid told Sky News: “This is intended to make a serious point about the bill and the huge infringement of liberty that entails and about the fact that this bill is going to do more harm than good.
“It’s going to make it harder for people to access education, it’s not going to reduce the number of people taking these things and the sensible solution has to be legal regulation of these drugs.”
Professor David Nutt, former drugs tsar and professor of neuropsychopharmacology, said: “It’s probably one of the safest recreational substances there has ever been.
“It’s been used for over 200 years, largely as an analgesic, a pain killer. It’s been used by writers like Coleridge and philosophers like James to get insights into the brain and now it’s being used by young people as an alternative to alcohol on the grounds that it’s a lot safer than alcohol and a lot shorter acting.
“So this desire to ban it is rather bizarre really.”
Addiction therapist Sarah Graham, however, said that it was a potentially addictive drug that needed to be controlled.
She told Sky News: “We do need this psychoactive substances bill because we can have a blanket ban and take down the internet sites and stop them being marketed at young people and so that the police can take some action because this has become a really big problem.”