Drug campaigners say around 1,000 people are set to attend a ‘festival’ celebrating cannabis at a south Manchester park.

The crowds are expected at the ‘420’ day at Platt Fields Park - one of a series of events to be held across the world on Sunday.

The event - now in its fourth year - aims to promote the campaign for the legalisation of cannabis and organisers have said they plan to smoke the drug in public, as they have in previous years. It is the first time that the event has been held in Manchester, the M.E.N. understands.

Police have warned organisers they do not condone the event at the park in Fallowfield and people seen using the class B drug will face arrest.

A Greater Manchester Police spokesman said: “Greater Manchester Police have not received any official notification of a planned event at Platt Fields Park on Sunday.

“Officers will be patrolling the area in conjunction with officials from the park and anyone seen to be actively breaking the law, will be dealt with in an appropriate manner.”

The Platt Fields event is organised by Manchester pro-cannabis groups ManCan and Mannijuana.

Organisers argue the drug should be legalised and say the gathering will be a ‘family friendly day’.

One member said: “Everyone smokes cannabis at the event but it is completely safe and no-one is there to cause trouble.

“It’s the only time when we condone smoking (cannabis) in public under the principal that for this one day we can become autonomous.

“It’s a family friendly day in the same way as taking your family to the pub for the afternoon. In society it’s frowned upon to have children around cannabis but when it’s treated respectfully there’s no problem.

“Cannabis is a safe drug, even compared with legal drugs such as alcohol and this is a day for those who enjoy it to come out and celebrate it.”

The term ‘420’ - pronounced four-twenty - is a code-term that refers to the consumption of cannabis and the ‘counterculture holiday’ on April 20 has been popular in the US since the 1980s.

A similar event in London’s Hyde Park is expected to attract more than 10,000 people.

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