Possessing laughing gas to get a psychoactive high became illegal in Britain on Wednesday, with serial offenders facing up to two years in prison and dealers up to 14 years.

The sale of small canisters of nitrous oxide has proliferated in recent decades, as young people in particular inhale the drug recreationally for a quick high.

Prolonged use can cause anemia, nerve damage, and spinal injuries, doctors warn, while the canisters have come to litter parts of urban and suburban Britain and been associated with anti-social behavior.

The ban, first proposed by Prime Minister Rishi Sunak's Conservative government in March and now imposed under the 1971 Misuse of Drugs Act, is part of a wider crackdown on lawlessness before an expected general election next year.

The ruling Tories appear to hope their traditional standing as the party of strong law and order policies can help them overcome a big polling deficit with the main Labour opposition. 

"Today we are sending a clear signal to people, especially young people, that not only is abuse of nitrous oxide dangerous to their health, but it is also illegal," policing minister Chris Philp said.

"For too long the use of this drug in public spaces has contributed to anti-social behaviour which is a blight on communities. We will not accept it," he added. 

He said that police now have "the powers they need to take a zero-tolerance approach to this crime," warning those caught possessing nitrous oxide "will face consequences".  

British law already bans the "knowing or reckless" supply of nitrous oxide for inhalation outside of medical uses. But the canisters have become easily available online and on the streets.

Under the new powers, possessing the drug with the intent to "wrongfully inhale it for a psychoactive effect" is an offense, the interior ministry said.

Those breaching the law could face an unlimited fine, a visible community punishment, or a caution visible on their criminal record. 

Serious repeat offenders could be jailed. 

The maximum sentence for production, supply importation, or exportation of the drug for unlawful purposes has been doubled, from seven to 14 years' imprisonment. 

Nitrous oxide has long been used in healthcare, catering, and other industries, and those with a legitimate reason for possessing the substance are exempt from the ban, the ministry noted.