If Britain were fighting a war where 2,000 people died every year, where increasing numbers of our young people were recruited by the enemy and our opponents were always a step ahead, developing new weapons faster than we could combat them, there would be outcry and loud calls for change. Yet this is exactly the situation with the "war on drugs" and for far too long we have resisted a proper debate about the need for a different strategy.

Last week, I travelled to Colombia with the largest delegation of UK businesses ever to visit the country. Our bilateral relations are growing stronger, exports are increasing and British businesses are making deals that will pay dividends for many years. Colombia is a country now realising its great potential, but it is also a country still coming to terms with its past. That includes, with its neighbours, still suffering from the debilitating and socially corrosive effects of the global drugs trade.

Colombia's president, Juan Manuel Santos, has already shown the kind of courageous leadership that the world needs to tackle this issue. He sponsored last year's influential drugs report produced by the Organisation of American States (OAS). In Bogotá last week, we discussed the study's findings and the call for more research of this kind, which approaches the drugs problem without preconceptions. We agreed on the need to widen the debate beyond the false choice between rapid legalisation of all drugs or military crackdown. Neither can solve the problem.

For Colombia, part of the solution is economic growth and reducing poverty. That is why it was so refreshing to be there announcing new business deals, a new direct flight to London and an expansion of educational co-operation.

To build on the progress it has made, Colombia's people need jobs. Young men need to know they can earn a living outside of the criminal gangs that have dominated their communities. Only then will the control and power of the cartels begin to wane.

The country now has a young, enthusiastic and creative generation entering the work force. They have to be given the freedom to succeed and set a new course for their country. This is why the peace process with Farc is so important. It has the potential to end one of the longest and most deadly conflicts in the world. This will take courage and compromise. But to have security there must also be zero tolerance for violations of human rights. I welcomed President Santos's commitment to this and to end the violence and harassment that have scarred Colombia's past.

The country is ready for change and I detected a significant shift in the public mood. I met former child soldiers, once recruited by guerrilla and paramilitary groups, and now enrolled in government programmes that help them start a new life. These were young men, who, at the age of 12, were forced into a horrific life. The criminal gangs had such a hold on communities that boys could only survive by joining them.

It was an incredible experience to talk to them and hear that for the first time they dared to imagine a brighter future, free from violence. They were studying, had access to healthcare and had jobs. Two were training to be nurses and another was going into the priesthood.

I also met representatives of Colombian human rights NGOs and Peace Brigades International: courageous individuals working to construct a more tolerant, inclusive society. All were clear about the central role of the drugs trade in perpetuating conflict and violence and the need to build a better future.

These experiences hammered home to me the reality that drugs are a global problem with victims all around the world. We can only tackle the harm they cause by working together with international partners such as President Santos and his government in Colombia.

Many people in Britain and the rest of Europe will still be unaware of the impact drug use in western nations has on countries on the frontline of the drugs trade. It is only right, then, that we play a part in helping to find a solution.

It is why I am a firm believer in the need for a royal commission in Britain and why I am so disappointed at my coalition partner's refusal to engage in a proper discussion about the drugs problem.

We should be led by the evidence of what works, not guesswork. That is why the OAS study is so significant and why Liberal Democrats in government are conducting a study of international alternatives. This is the first proper UK government report examining the different approaches in other countries.

I believe there is an increasing critical mass of international voices, in Latin America and in Europe. They are saying we've got to think anew and mustn't be limited by our blinkered view about what the approach was in the past.

No country can solve this problem alone. The UN has agreed to hold a special session on drug law reform in 2016. It cannot come soon enough. The current UN drugs conventions badly need revising. I want European countries to work together to agree a common position in favour of reform to take to that discussion in 2016. The UK can lead the debate in Europe and Europe can lead the debate in the world. But we must be prepared to start afresh with a new mindset and be prepared to do things differently.

The status quo is failing. One in five young people has admitted taking drugs in the last year. Cocaine use has more than trebled since 1996. Every time someone dies of an overdose, it should shame our political class. One thing we must do is break the link between addiction and crime. If we treat addiction as a health issue, we can free the addicts from the criminal gangs that blight their lives and our communities.

I want to end the tradition where politicians only talk about drugs reform when they have left office because they fear the political consequences. This has stifled debate and inhibited a proper examination of our approach.

We need to bring this issue out into the open and to be led by the evidence of what works. We owe it to our young people, to the families torn apart by addiction and to the states that look to us for leadership and advice. We can help countries such as Colombia break the stranglehold of the drug lords once and for all.

The choice we have to make now is how we do things differently. Repeating the mistakes of the past is not the way to solve this problem in the future. Put simply, if you are anti-drugs, you should be pro-reform.