Spanish Benedictine nun is emerging as one of the most outspoken – and atypical – leaders of southern Europe's far left

The speedometer on Teresa Forcades' battered silver Peugeot saloon shows 130kmh, but Spain's most famously radical nun is so busy talking she seems oblivious to the 80kmh speed limit signs above the motorway near her Sant Benet convent on the slopes of Montserrat, Catalonia's sacred mountain.

The woman whose biting criticism of everything from banks to big pharmaceutical companies has shot her into the political limelight is rushing to Barcelona's train station so she can travel to Valencia to deliver a speech. Then she will fly to the Canary Islands for the next appointment on her public speaking schedule.

She is on the campaign trail to promote a radical manifesto for revolutionary political change (link in Catalan). In the black headdress of the Benedictine order, Forcades has emerged as one of the most outspoken – and atypical – leaders of southern Europe's fragmented, confused far left.

Flooring the accelerator, she praises Syriza, the leftwing Greek group that rose from the rubble of the country's ruined economy and is a reference point for her manifesto for a radical approach to building an independent Catalonia.

"The economic crisis in Spain has got to a point where it threatens the fabric of society," she says. "This is something that has happened in Greece. The precariousness of people's lives is progressing at an accelerated pace and they cannot cope. The danger of violence and upheaval in some non-democratic way is a possibility."

She and economist Arcadi Oliveres co-wrote the manifesto calling for a refounding of the Spanish state, with an independent Catalonia, nationalised banks and energy companies and an exit from Nato. They hope to rekindle the spirit of the indignados who occupied Spanish squares in 2011, but focusing on more concrete aims.

"I and a group of people felt a need to intervene, in my case because of this popularity I've acquired. I thought it could be good to try to organise this discontent, this feeling of deep disappointment and growing tension," she says. "I'm not starting a political party and am not intending to run in any elections. That is not for a Benedictine and not for me."

While she is not running for office, Forcades is not shy of public debate, regularly appearing on local television. Her conversation includes references to liberation theology, Marx's theories on surplus value, Hugo Chávez's Venezuela and the Tobin tax, as well as the 12th-century figure Saint Hildegard of Bingen or the rule of Saint Benedict, precepts by which she tries to live.

Visiting Venezuela in 2009 she found a country she did not recognise from critical descriptions in Spanish newspapers. "Marginalised people spoke as if what they thought and wanted was important in the politics of their country," she says. "They had a sense of counting, which is essential in democracy."

Her critique of neoliberal capitalism includes not just a Christian desire to protect the weak, but also an attack on the hypocrisy of a system that gives goods and capital the freedom to cross frontiers while workers cannot. "It is a version of capitalism where the rights and needs of people are pushed aside," she says, pointing to how taxes are higher on selling bread than on financial speculation.

Her fame stems from a polemical spat with the World Health Organisation and the pharmaceutical industry over swine flu vaccines in 2009. A video filmed at her convent, in which she talks to camera for a solid hour about what she claims are the dangers of the vaccine, went viral.

"What I found astonished me, the lack of scientific ground for any of the public policies and decisions," she says. "The video was highly viewed by more than one million people. And that was the start of my public presence."

El País labelled her a "paranoid conspiracist" and "hoaxer-nun" who used half-truths and her religious status to spread fear. But Forcades, who trained as a doctor in the US and has a public health PhD, says she spent three months studying the science before making an hour-long YouTube video, one of 95 that now sit on a Forcades YouTube channel.

Forcades hopes to revive the spirit of Spain's 'indignados' protest movement. Photograph: Lluis Gene/AFP/Getty Images

"The campaign was not based on scientific fact, but was orchestrated to favour the industrial interests of the big pharmaceutical companies," she says. It was also an attempt to curtail rights, she claims. "That was the talk, to justify mandatory vaccination."

At Barcelona's Sants railway station a middle-aged man walks up to her and kisses her hand. A woman with blonde frizzy hair also greets her like an old friend. Does she know them? "No, I don't." Does this happen often? "Yes."

A Barcelona vox pop gives mixed results. The young and working class do not know her, or mumble vaguely about vaccines, but middle-aged, middle-class Barcelonans know all about her and, mostly, approve. However, some question how she can be both a leftwing feminist and part of a misogynist church that bans contraception and backs punishment for abortion.

Before she took her vows in 1997, Forcades tested the other nuns by giving a talk on a group of gay Catholics who celebrated their sexuality as a gift from God. She was humbled by the nuns' humane reaction and, so, joined them.

Having already studied medicine in Barcelona and New York and signed up for a masters in theology at Harvard, the nuns encouraged her to finish her studies then join them as a resident public intellectual, eventually giving her a secretary and freedom to travel and study elsewhere.

Forcades does not find convent life oppressive. "The myth that women can't fix a tap quickly disappears when there are no men," she says, pointing out that, historically, women often enjoyed greater freedom behind convent walls than in the real world.

And she does not bite her tongue on the church Pope Francis took over in March, arguing for women priests while leaving contraception and abortion to individuals' consciences: "The Roman Catholic church, which is my church, is misogynist and patriarchal in its structure. That needs to be changed as quickly as possible."