'Weed smokers will be punished according to the Korean law,' senior police officer says South Korean residents who smoke cannabis in Canada will be “punished” on their return home, the country's authorities have warned.

The North American nation became the second country in the world after Uruguay to legalise recreational marijuana last week, a move that has triggered global debate around decriminalisation of the drug. But South Koreans living in there were told earlier this week to stay away from the drug.

"Weed smokers will be punished according to the Korean law, even if they did so in countries where smoking marijuana is legal. There won't be an exception,” said Yoon Se-jin, head of the anti-drugs division at Gyeonggi Nambu Provincial police agency.

Those found guilty could face up to five years in prison. Korean police also said they plan to hold workshops in Canada and Uruguay to make clear the risks of smoking cannabis in the two countries, The Korea Timesreported.

Around 23,000 Koreans with student visas are living in Canada, according to ministry of foreign affairs data.

All of South Korea’s laws apply to its citizens no matter where they are in the world and those breaking them can theoretically be prosecuted on their return to the East Asian country. In contrast, Britain’s former chief police officer has called on the government to look into legalising cannabis.

Sir Bernard Hogan-Howe has called for an urgent review of the evidence and said the Home Office must reconsider its position on the drug following Canada’s legalisation.  “If I was home secretary, I would have an urgent commission of experts to look at the evidence about what’s happening about cannabis in North America,” Sir Bernard told Channel 4’s Dispatches programme.

The Home Office has insisted decriminalisation of cannabis “would not eliminate” illicit trade or the harms caused by drug addiction.