Should Cannabis Be Legalised? — A write-up

June 26, 2012

(This is a write-up of the mini-documentary, click here to watch.)

Cannabis is the most widely used illegal drug in the world – it is used regularly by hundreds of millions of people, and many more have used it at least once – including several politicians, with some going as far as to say they have actually inhaled it.[1] According to several government-sponsored studies, it is less harmful than alcohol and cigarettes.[2] Many prominent public figures have called for its legalisation, or at least decriminalisation. And yet it continues to be illegal in many western countries.

By keeping it illegal in the UK, are we needlessly handing over a multi-million pound industry to criminals when it could be controlled – and taxed – by the government?[3] By spending time and resources on policing cannabis prevention are we wasting precious government money?[4]

To many, it seems crazy that cannabis is still illegal. But are there good reasons why? Would making it legal lead to an increase in its use, with more people suffering its side effects – whether physically, mentally, or as a society? Would it become a gateway to harder drugs?

Because no country has completely legalised cannabis, there is no sure way to tell.[5] There are, however, countries where they have been more lenient and these can help us predict what might happen. This mini-documentary looks at what happened to Lambeth in south London when it ‘depenalised’ cannabis use between 2001 and 2002. The results of a new study by Jérôme Adda, Brendon McConnell and Imran Rasul provide some clear answers while also posing deeper questions.[6]


Between July 2001 and July 2002, the London Borough of Lambeth ‘depenalised’ cannabis. This means that so long as the cannabis was for personal use, police would only remove the drugs and issue a warning. There would be no arrests or prosecutions. The scheme was designed to save police time and money so they could focus on other crimes.[7][8]

The policy was initially designed for six months but following an independent poll showing broad public support for the scheme, it was extended for a further six months.[9] Yet in those six months, media support for the scheme turned – there were reports of children being sold cannabis outside school – and political pressure grew to scrap the scheme.[10] The scheme came to an end in July 2012 (at around the same time as cannabis was re-classified from a Class B to a Class C drug, which has since been reversed).[11][12]

Ten years later, economists looked at the effect of the policy on crime. They compared the number of arrests and the number of prosecutions by the police in Lambeth with other areas of London before, during, and after the policy.[13] The study uses detailed records taken directly from the London Metropolitan Police for all 32 London Boroughs, for each month between April 1998 and January 2006.[14] The findings reveal how complex the issue is and go some way towards understanding why we have the current crazy situation.


Crime rates for cannabis possession went UP by around 20%.

The number of arrests for cannabis possession went up by 18%.This more than off-sets the fall in arrests because of the change in policy. Moreover, cannabis possession is still higher well after the policy experiment ends. Over the same period, there is no evidence of a London-wide increases in cannabis crime rates.

By looking at the neighbouring boroughs, the researchers estimate that a large chunk of this increase (as much as half) is due to people coming from nearby to buy and smoke cannabis in Lambeth – so-called ‘drug tourists’.

The rest of this rise is caused by a combination of a) cannabis users buying more cannabis, b) new people starting to using cannabis, and c) police reporting arrests where they would otherwise not have done.

But other sorts of crime went DOWN by 11%.

Other crime fell by 11% compared with the London average (including adjustments for factors such as the number of unemployed people). Even once we account for the rise in cannabis possession offences, there is a fall in overall crime by 8%. Crime fell in areas such as violence against the person, sexual offences, robbery, theft, fraud, and criminal damage – these account for 97% of crimes in Lambeth. Meanwhile arrests went up by around 3% and prosecutions also went up. In other words, by not having to focus on cannabis, the police were much, much more effective, just as the policy had intended.[15]

And yet the policy was abolished.

Was there something people didn’t like about depenalising cannabis that wasn’t being picked up by the survey or in the crime statistics?

House prices in Lambeth were affected.

The study also finds that house prices in Lambeth were up to 6% lower than they would otherwise have been. House prices are a way of economists measuring how much people want to live somewhere. Usually we would expect lower crime to have a positive effect on house prices as the place becomes a more desirable place to live, but it seems that many people did not want to live somewhere where cannabis is depanalised – or they were only willing to do so at a lower price.


So despite many people being in favour of depenalisation according the polls, there was a sense of ‘not in my backyard’. This is something economists often see in people’s behaviour: people say they believe one thing, but their actions suggest otherwise.

Is this because of perception rather than reality? Did people have a genuine, well-informed fear of what cannabis depenalisation was doing to Lambeth, perhaps as a place to bring up children? Or were they just reacting to sensationalist claims by the media? It remains a mystery.

Whatever it was, there is something in how people behave that would suggest that – for better or worse – there are still concerns to be overcome before a radical change in drug policy in the UK – or elsewhere.

This mini-documentary cannot hope to provide the answers. Its humble aim is to contribute to the debate.

Bob Denham

June 2012

Produced by ECON FILMS

Camera Operators: George Featherby, Greg Luscome & Bob Denham

Music: Andrew Warne

With thanks to: Max Mallows, Imran Rasul, Anthony Sturgeon, Romesh Vaitilingam, Daisy Whitaker and the Royal Economic Society

Producer: Claire Coutinho

Written and Directed by Bob Denham



[1] There are an estimated 250 million drug users worldwide according to the UN. An estimated 162 million people used cannabis in 2004. The United Nations Office on Drugs Crime (UNODC) estimates that it accounted for around 80% of illegal drug use in 2004, suggesting that hundreds of millions of people use it regularly (see UN document here).

[2] In 2009, Professor David Nutt, the UK government’s drug adviser was sacked for claiming that, among other things, cannabis was less dangerous than alcohol and tobacco. He also said that the chances of schizophrenia from cannabis use were around 1 in 5,0000. (see for example in the Guardian here).

[3] The UN estimates that the cannabis market in the US is worth up to $60 billion (see here). The UK is likely to have a market that is a similar relative to its population and the size of its economy.

[4] According to Brian Paddick (London Mayor Candidate 2012), London Metropolitan Police spend £24 million on cannabis policing each year (see here).

[5] Cannabis is illegal in the UK, Canada, and most US states and European countries. It is depanalised in Spain, Portugal, the Netherlands, Italy, much of South America, parts of Australia, and 16 US states (see Wikipedia here).

[6] Adda, Jérôme, Brendon McConnell, Imran Rasul (2011), “Crime and the Depenalization of Cannabis Possession: Evidence from a Policing Experiment”, Working Paper. Paper presented at the 2012 Royal Economic Society conference.

[7] For a review of the Lambeth Cannabis Warning Pilot Scheme carried out by the Metropolitan Police Authority in 2002 see here.

[8] The Lambeth Cannabis Warning Scheme was introduced by the police commander for the London borough of Lambeth, Brian Paddick, after consulting with staff on drug policing. Brian Paddick later ran for Mayor of London in 2008 and 2012 representing the Liberal Democrats. In the most recent election he offered to depanalise cannabis across London, see here. He even had a poster.

[9] An IPSOS-MORI poll was commissioned during the six-month policy experiment. This found broad local support for the scheme. 36% of surveyed residents approved outright of the policy. A further 47% approved provided the police actually reduced serious crime in Lambeth. Only 8% disapproved of the scheme. See here.

[10] See criticisms from senior Tories and Labour as reported by the BBC here.

[11] In part due to disagreements between the police and local politicians over the policy’s true impacts, post-policy Lambeth’s cannabis policing strategy did not return identically to what it had been pre-policy. Rather, it adjusted to be a firmer version of what had occurred during the pilot. The MPA announced that in Lambeth officers would continue to issue warnings but would now also have “the discretion to arrest where the offence was aggravated. Aggravating factors included: (i) if the officer feared disorder; (ii) if the person was openly smoking cannabis in a public place; (iii) those aged 17 or under were found in possession of cannabis; (iv) individuals found in possession of cannabis were in or near schools, youth clubs or children’s play areas”.

[12] See Evening Standard and BBC here and here.

[13] This technique is called ‘difference-in-difference’. It tries to emulate a laboratory experiment. In a scientific experiment, we would give the treatment to one group of people and compare this with group of similar people who did not receive the treatment – known as the control group. In the real world this is rarely possible, instead economists compare one ‘treatment’ group – in this case Lambeth – with others in a ‘control’ group – in this case the neighbouring boroughs of Croydon, Merton, etc. They then look at the difference in how these boroughs have changed: the ‘difference-in-difference’.

[14] The study also had data on the number of criminal offences related to any given drug type, e.g. cannabis, heroin, cocaine etc. They also had, for each drug type, data on the specific offence committed: possession, trafficking, intent to supply etc.

[15] These results are the same whether arrests and prosecutions are measured as a fraction of crime or as being per 1000 of the adult population. Hence these patterns in arrest and prosecution rates likely reflect real changes in police behaviour rather than being driven by falls in the number of offences in each crime type.