If you really want to legalise cannabis, then why on earth would you go and get high in a park?

Embarrassing displays of public consumption like the 420 celebrations are not going to lead to meaningful drug reform, but I know what will

A man enjoys the "420 Day" pro-cannabis rally in Hyde Park this weekend (ZUMA/REX)

Thousands of people gathered in Hyde Park yesterday to mark the yearly event of 420, and protest against the UK's cannabis laws. 420 is an American code word for cannabis with very esoteric, bizarre and not very interesting origins. However, what it means is that on 20 April at 4.20pm, some cannabis users take the opportunity to protest and demonstrate.

I'm all for drug reform. But I'm also completely against these sort of events. Not only do they not work, but they actually damage the cause and hold back reform.

The prohibition of cannabis is an irrational, unjust and deeply damaging policy that causes far more harm to our society and to individuals than cannabis ever has. It creates a massive £6bn criminal market, consumes £500m each year in law enforcement costs, and ruins the prospects of people with criminal convictions for choosing to use a substance which is scientifically proven to be much less harmful than alcohol or tobacco.

Even worse than this is the denial of access to medicinal cannabis for those in pain. suffering and disability. This isn't just an injustice – it's an obscenity, and in my opinion the politicians who stand in the way have blood on their hands.

And reform elsewhere has already proved to be a roaring success. In America, legalisation has led to underage use declining, crime rates falling, and traffic fatalities decreasing. What's more, cannabis-friendly states are now reaping massive new tax revenues, which are funding hospitals and schools with money that would have previously lined the pockets of criminals.

So I can understand the frustration that encourages people to protest, and smoke en masse in public spaces. After all, I used to be one of them only three years ago. But eventually my colleagues and I decided to take a different approach, and began actually engaging with the Government.

In the last 18 months we have made more progress than any drugs reform campaign has made over 50 years. We have met with a succession of government ministers, senior politicians and select committees. We have changed minds in a way that has never happened before. We have provided briefings to Nick Clegg and his advisers, and the Lib Dems have even adopted our policy on medicinal cannabis word for word. And you may be surprised, but between the two main political parties, there is now more support for reform among Tories than Labour politicians.

What we've discovered is that working with system rather than against it can be hugely effective. On the other hand, protests and demos only help reinforce the negative stereotypes of cannabis users that the media and politicians have used to demonise us for so long. Seizing control of a public space to smoke cannabis is simply crazy. There are always young teenagers or children involved, and although the general public has been subject to false propaganda and misinformation about the drug, it only serves to make people more alarmed.

What people need to realise is that cannabis isn't a niche hobby pursued by a small number of people who enjoy listening to reggae. Neither is it a culture or lifestyle in itself. There are 3m regular cannabis users in the UK who do not want to be seen as some sort of rebellious group isolated from the rest of society. The small group of "stoners" that we are seeing on the news don't represent them at all.

Also, the UK is home to a self-serving group of researchers who regularly churn out almost identical "studies" on the harms of cannabis which are not reflected in the facts of actual healthcare records. Quite correctly, the UK attitude to cannabis is regarded as hysterical throughout the rest of Europe, Israel, Canada and the USA, where wiser counsel and evidence prevail.

So, for those who want to see reform, which should be everyone who supports a more effective drugs policy, embarrassing displays of public consumption are counterproductive. We are now winning this argument through considered, diligent and professional lobbying. The "free the weed" stoners, anarchists and revolutionaries are the enemies of progress. The way forward is to meet with your MP, present the facts and insist that policy is based on evidence rather than prejudice and media hysteria.

Peter Reynolds is the leader of CLEAR Cannabis Law Reform. To find out more go to: http://clear-uk.org/