Cannabis protesters have gathered in Hyde Park at an annual demonstration which calls to end criminilisation of the drug.
Large crowds flocked to the central London park throughout Wednesday for this year’s 420 protest.
Organisers encouraged visitors to bring banners and a picnic for the event which attracted a thousand people last year.
Campaigners said they believes attitudes towards the drug had changed with hopes it could be legalised in the future.
Lee Harris, London mayoral candidate for The Cannabis is Safer Than Alcohol party (Cista), said he had seen a huge change in opinion over the past 50 years.
He said: “There has been a paradigm shift in public opinion and not just in this country.
“I think things are going to happen. We have many of the police forces on our side who think prohibition did not work.
“The war on drugs was an utter failure and caused so much harm in our society.
“Cannabis should be regulated, legalised and taxed.”
The term 420, which has now become a code word, was apparently coined in 1971 by a group of teenagers in California.
The Met Police said 20 people were arrested for a “variety of drug offences”.
One 27-year-old woman was been arrested on suspicion of possession with intent to supply a class A substance, 19 people were arrested for possession of cannabis, and 12 more were issued with cannabis warnings.
