Amanda Feilding, the countess of Wemyss and March, is being taken seriously in her quest to change drug policy across the world after years of being portrayed as an eccentric aristocrat

The proud owner of a country estate and an aristocratic title, Amanda Feilding, Countess of Wemyss and March, might seem an unlikely campaigner for the reform of laws criminalising recreational drugs. But no one can say she hasn't put the hours in.

For the past 15 years, as part of the Beckley Foundation, which she set up in 1989, Feilding has hosted seminars, promoted research and lobbied the powerful in the name of legalisation. At one stage the Daily Mail became sufficiently alarmed to ask: "Is the countess just an amusing and irrelevant eccentric? Or could she be a real danger to society?" Feilding was clearly amused by that suggestion.

On 5 December, she will oversee the launch of a new global initiative to deal with what she tells the Observer is "the real danger to society" – a counterproductive war on drugs that allows a deadly criminal culture to thrive across the globe.

With the support of an array of politicians, stars, academics and artists, the campaign will be launched with a documentary film, Breaking the Taboo, at Google's premises in London and New York. It is supported by Virgin and by Avaaz, a campaigning community with 16 million members. The website asks people to recognise that the war on drugs has failed and that the cost of fighting it is unbearable for many countries, while the availability and range of drugs increases every year. It asks people to urge governments to promote new policies based on scientific evidence.

Supporters include former presidents of Brazil, Colombia, Mexico, Switzerland, Poland and the US, and Feilding hopes that a fundamental global review of drugs laws is closer than ever before.

"For 15 years I have been working away with opinion-formers," said Feilding. "But now it is time to get politicians onside. Politicians will not move unless they are driven by the people. We need a grassroots movement of people saying that our children will be better looked after if the government regulates the supply of drugs, rather than leaving it to criminals.

"It has been a long journey, but I think the climate is fundamentally different from even two years ago. We are on the cusp of a big change."

Breaking the Taboo tells the stories of addicts and random victims of drug gang violence. It also features the former president of Colombia, César Gaviria, whose brother was kidnapped and sister murdered.

Change is coming, Feilding believes, because the belief that drugs policy is not working has gone mainstream. "Now it's people like Kofi Annan, Jimmy Carter and the president of Guatemala saying it's time for a change," she said.

Earlier this year Feilding was invited by Otto Pérez Molina, the president of Guatemala, to advise the government on drugs policies that will cut the level of drug-related violence and corruption that blight the country. Guatemala is one of many transit countries in Central America where rival gangs compete and bribe officials as they move cocaine and other drugs from South America to the US.

Feilding's journey to the forefront of the campaign to reform drugs policy began in 1960, when she first smoked cannabis at Oxford University, beginning a lifelong fascination with the benefits of altering the consciousness and a desire to understand the dangers.

Her foundation undoubtedly has its radical side, exploring the idea that some drugs could enhance understanding and creativity. A major part of the foundation's work has been to fund experiments into the use of psychoactive drugs. That research – carried out at Imperial College and University College, London, and Johns Hopkins University in Baltimore – has suggested that MDMA, LSD and psilocybin (the active ingredient in magic mushrooms) can all have benefits for psychological health.

"In this time when there is so much psychosis, depression and post-traumatic stress disorder, the NHS cannot afford to give everyone two years of therapy. We need to find better and faster ways to treat people and psychoactive drugs with skilled therapists could be the answer," she said.

However, the main concern has been the question of legalisation. The Beckley Foundation has consistently promoted the reform of global drugs policy, using money raised from donors such as the financier George Soros. Regular policy seminars have taken place in the House of Lords and featured scientists and policy specialists from all over the world.

Some of those talks led to unwanted headlines. The government's adviser on drugs, Professor David Nutt, was forced to resign when he suggested at a Beckley event that alcohol and tobacco were far more dangerous than cannabis and, in a separate incident, said taking ecstasy was no more dangerous than horse-riding.

Perhaps conscious of how her past may be perceived, Feilding emphasises that she believes in the strict regulation of drugs rather than nonregulation. "We are not talking about selling things in Tesco. There should be no advertising and no selling to minors. Some things might only be sold on prescription," she said.

Her vision of Britain includes cannabis farmers' markets, such as in Barcelona; the prescription of heroin for addicts, as takes place in Switzerland; or the use of psychoactive drugs for marriage counselling, which has happened in the US. "Right now we have a completely unregulated market controlled by criminals. Everyone would be much safer in a regulated society than the unregulated one that exists now," she said. After 15 years making the argument, Feilding thinks the world might finally be listening.