Police arrested 53 people as pro-cannabis protestors gathered to get high and call for the drug to be legalised in London 's Hyde Park today . Dramatic images captured the moment four officers took down and restrained a tracksuit-wearing man near the entrance to the park - just yards from a prominent police sign which read : 'Possession of cannabis is illegal ' . The crowds met this afternoon as part of the annual '420 ' event - a global celebration of cannabis which calls for reform to drug laws . Scroll down for video . Taking him down : The four police officers were seen rushing towards the man at the entrance to Hyde Park . Restrained : The pro-cannabis protestor is pushed down to the ground just yards from a police sign reading : 'Possession of cannabis is illegal ' Thousands of campaigners were seen sitting on the grass openly smoking marijuana , comparing the size of their joints and listening to speakers while dozens of police officers hovered nearby . Many protestors handed out cannabis leaf-shaped fliers and carried signs , with one reading : 'Ed Miliband would n't want his own children criminalised for cannabis possession . ' Of the 53 who were arrested in London , 16 were taken into custody , while 21 were released on street bail and asked to return to a station at a later date . A Met Police spokesman said : 'Anyone seen by an officer openly smoking cannabis in Hyde Park or in the Westminster area could be issued with a warning or face arrest . ' The term '420 ' has become universally known as the code word for cannabis - after a group of students coined it while searching for an abandoned crop of marijuana in California in 1971 . A man wearing a President Obama mask holds a marijuana joint to his mouth in Hyde Park today . Campaigners were seen openly smoking cannabis while dozens of police officers stood nearby . The festival is usually held on April 20 and last year there were estimated to be around 10,000 people openly smoking marijuana in Hyde Park . The 420 Day event is organised by a reform-seeking group called NORML UK , along with the UK Cannabis Social Clubs ( UKCSC ) . Last year , Greg de Hoedt , president of UKCSC , told the Guardian last year : 'The cannabis community is crying out for legalization and regulation . 'We encourage growers to register with UKCSC because we want data we can present to authorities and say : this many people grow cannabis , this many people are growing for medicinal purposes ; and we can also establish which strains work with which illnesses . ' Four people hold their marijuana joints together with a bag full of the drug visible in the centre of the photo . Many campaigners carried signs including this message referring to Labour Leader Ed Miliband . This weekend also saw campaigners gather in Glasgow 's George Square and in Manchester 's Platt Fields Park . The Manchester event 's Facebook page reads : 'This will be our fifth annual gathering so we plan to make it one to remember . 'For those who have n't been there 's going to be good tunes , good food , good company , games and activities , face painting , freebies , talks stalls and information all in the name of celebrating the many aspects of cannabis culture . ' Checking for drugs : Police officers stop and search a visitor to Hyde Park this afternoon . The 420 Day event is organised by a reform-seeking group called NORML UK , along with the UK Cannabis Social Clubs ( UKCSC ) A protestor blows smoke from a marijuana joint during taday 's pro-cannabis festival in Hyde Park . More than 50 people were arrested at today 's event in London , with 16 taken into police custody . The controversial pro-cannabis event is set to continue into tomorrow with a 'Parliament Protest Picnic ' , according to the 'London 420 ' Facebook page . This weekend also saw campaigners gather in Glasgow 's George Square and in Manchester 's Platt Fields Park .
Thousands met in Hyde Park annual as part of today global '420 ' event . Crowds seen openly smoking marijuana as police officers stood nearby . Controversial festival also saw gatherings in Manchester and Glasgow .