'We've got to take action': PM teases 'decisions' to come on outdoor smoking ban

Both women are visibly high and still giggling as two officers jump out of their car. Their mission: a targeted operation to catch people suspected of inhaling banned laughing gas.

"I've just seen a couple of balloons, so we believe you've been using nos," one of the officers, Spelthorne Borough Commander Matthew Walton, tells the women.

Since November, nos - nitrous oxide, commonly referred to as laughing gas - has been categorised as a Class C substance and banned for recreational use.

Prosecutions can lead to a two-year prison term.

But data from 22 police forces across the UK, put together by Sky News, reveal that fewer than 78 arrests were made for nitrous oxide possession in the first three months of the ban - and 16 people were charged.

'No laughing matter'

The police conducting the operation last month in Staines had been tipped off by a local litter-picking organisation about nitrous oxide hotspots.

The officers find used balloons and a large box containing several large canisters of nitrous oxide. Suddenly, no one is laughing anymore.

A female officer conducts body searches. Up on the fence next to the women a sign warns of a £1,000 fine for anyone using nitrous oxide. "No laughing matter," it reads.

Neither woman is arrested or charged; instead the driver, who appeared to be in her late teens, is offered a voluntary attendance interview.

"Depending on what she says we'll make a disposal decision which could be a police caution, referral to Checkpoint (education on drug-driving) that they have to pay for themselves, like a speed awareness course," says Commander Walton. "Or it could lead to a charge."

Police say they are trying to strike a balance - but also be aware of the risks surrounding the gas.

"We've obviously got to balance it against all our other priorities," Commander Walton told Sky News, emphasising the need for police to be proportionate in their response to young people out having fun.

But he warned that nitrous oxide could lead to other, more serious crimes.

"I think there is degree, especially with the age of the people we've got here, that where nos goes, cannabis follows. And sometimes harder drugs."

Notting Hill Carnival

Three friends sit on the side of a pavement at the Notting Hill Carnival. A barbecue throws smoke up in the air and children play next to a stall selling chicken and rice.

One of the friends is holding a silver balloon in her mouth and almost doesn't notice when it whizzes away as she smiles. Straight away, she pulls out another. It's noisy at Carnival but you can still hear the hiss of the balloon being gassed up.

A big silver canister sits between her legs and she laughs with friends when they realise they've been spotted by the Sky News camera. The nonchalance doesn't go away even when three police officers walk in their direction.

But the officers walk on by, despite seeing the group doing balloons. A few moments later a patrol car also rolls by slowly. Still, no intervention.

Some 7,000 police officers were deployed to this year's Notting Hill Carnival, the UK's largest annual street party.

The Metropolitan Police said officers prioritised offences which posed a more immediate risk.

But it led to questions from drug policy experts about whether a ban on nitrous oxide was justified in the first place.

'Things may have got worse'

"Prohibitions generally can mutate behaviours and markets, but what they don't do is stop people taking drugs," said Steve Rolles, senior policy analyst at Transform Drug Policy.

Mr Rolles explained that the law is working to reduce the public profile of nitrous oxide in big events which are subject to high surveillance.

Indeed, discarded canisters from Carnival were down by roughly half this year. But Mr Rolles explains that it could mean repeat users carry on misusing in private, unsupervised spaces, and warns of another, potentially more dangerous consequence.

"If the result is to push people from nitrous oxide to other more harmful drugs then that's not really a public health win.

"You might have a lot less litter but from a public health point of view things may have got worse."

Mr Rolles added: "You can see how policymakers may try to mark this ban as a success but these things tend to displace the problem - either geographically where users carry on somewhere else - or they move to drugs which they can use in a more inconspicuous way.

"More drinking, more cannabis, more ketamine. And probably more dangerous."

-SKY NEWS