Middle-class cocaine users are inconsistent hypocrites if they fail to recognise the environmental and social damage their drug use is inflicting on producer countries, the Colombian president has said during a visit to London.

In an interview with the Guardian on Monday, Iván Duque said that cocaine’s social acceptability had to end. “There are many people who present themselves as environmentalists, and if they want to be coherent, they must understand all the environmental damage that is caused by the production of cocaine – not just destroying tropical forests, [but] spreading chemicals in protected areas and destroying human capital,” he said.

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Duque said that cocaine production leads to the destruction of thousands of hectares of tropical forest. “It’s not just big social damage, but environmental damage. How can you present yourself as a defender of the environment when you are creating so much harm? There needs to be an end to hypocrisy and inconsistency,” he said.

Asked what he thought of admissions by prominent British politicians – including the Conservative leadership candidates Michael Gove and Boris Johnson – that they have used cocaine, Duque said: “The issue with illegal drugs is, they not only have a bad effect on your health, but potentially on third parties. It’s not advice to candidates. Its advice to human beings.”

However, Duque also pledged to relaunch the aerial spraying of coca crops with herbicides within weeks – a process that has been widely criticised by farmers for devastating legal crops alongside illicit plantations.

Colombia suspended the aerial fumigation of coca, the raw ingredient in cocaine, in 2015 after the World Health Organization linked the herbicide glyphosate to cancer. The decision was later backed by the country’s constitutional court.

Facebook Twitter Pinterest Members of London’s Colombian community protesting in the City against the visit by Iván Duque. Photograph: Damien Gayle/for the Guardian

The US, frustrated by surging cocaine exports, has pressured Duque to resume aerial spraying and threatened to decertify Columbia as a partner in its war on drugs.

Duque said he was considering tougher measures against coca growers – not to please any third country, but because it was his country’s “moral responsibility to act”.

Colombia remains the world’s largest producer of cocaine exports, and a recent UN report said the total acreage under production was an estimated 17% higher in 2017 than 2016.

The drug trade has flourished despite the 2016 peace deal with the guerrillas of the Revolutionary Armed Forces of Colombia (Farc). That accord was supposed to usher in a peaceful new chapter, but violence still rages as dissident rebel factions and rightwing paramilitaries battle for control of coca-growing territory once controlled by Farc.

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Activists and social leaders have been targeted at unprecedented levels: 702 have been murdered since the peace deal was signed, while 135 ex-combatants have also been killed.

As Duque met potential investors in the City of London, protesters nearby laid the names of hundreds of murdered social leaders, human rights defenders and trade unionists along the pavement of Threadneedle Street.

Miriam Ojeda, originally from Cali, Colombia, who now lives in Denmark Hill, said Duque had betrayed the terms of the peace deal with the Farc. “All the institutions for peace have been sabotaged systematically,” she said.

“The government is telling the business community that everything is good in Colombia, but in fact these people have been killed since the peace agreement has been signed … Communities in Colombia are facing violence on a daily basis.”

Facebook Twitter Pinterest Names of murdered social leaders, human rights defenders and trade unionists were displayed in protest at Duque’s ‘betrayal’ of the terms of the peace deal with the Farc. Photograph: Damien Gayle/The Guardian

Duque was relatively unknown until he won the presidency in Colombia last year after spending most of his adult life in Washington DC, working at the Inter-American Development Bank.

A rightwinger naturally allied to Washington, Duque has played a prominent role in the international effort to oust Nicolás Maduro, as the deepening crisis in neighbouring Venezuela has sent at least a million migrants across the border between the two countries.

Duque was one of the first Latin American leaders to recognise the opposition leader Juan Guaidó, who declared himself Venezuela’s rightful ruler in January. In March Duque declared that Maduro was “facing his last days”, but since then the opposition campaign has faltered.

“The current dictatorship has been in power for almost two decades and will not end overnight, but I think this time the diplomatic blockade has made the dictatorship the weakest it has ever been,” he said on Monday.

“It could take a day, a week, a month. [Maduro’s] military forces are broken, and day by day more of the military want to be on the right side of history. He is surrounded by people that any moment can turn their back on him. The three conditions are clear. We need an end to the dictatorship, a transitional government, and free and fair elections.”

Donald Trump and his hawkish national security adviser, John Bolton, have repeatedly warned that military intervention remains an option in Venezuela, but Duque warned against such measures. “A foreign military option [would be] very costly and very complex. The only viable way to put pressure on Maduro to step down and end this is for the military to put itself on the right side of history,” he said.