Extinction Rebellion wants non-violent civil disobedience to force governments to avert a climate crisis it says will bring social collapse

* Extinction Rebellion leader mulls mass debt refusal

* Looking at Britain-wide protests in major cities

* Psychedelic epiphany gave inspiration for group

By Guy Faulconbridge and Andrew R.C. Marshall

LONDON, May 1 (Reuters) - After paralysing parts of London, the co-founder of environmental group Extinction Rebellion has a message for the world: We've only just begun.

The group disrupted London with 11 days of protests that it cast as the biggest act of civil disobedience in recent British history. Iconic locations were blocked, the Shell building defaced, trains stopped and Goldman Sachs targeted.

The aim: A rebellion against the political, economic and social structure of the modern world in time to avert the worst devastation outlined by scientists studying climate change.

So what's next?

For the next phase of what she describes as "a movement fueled by love", Gail Bradbrook, a co-founder of Extinction Rebellion, told Reuters she wanted to provoke a mass refusal to repay debt that would upend the financial system.

"Economic growth tends to require the taking of resources from the Earth. So something has to change on a debt-based economy," said Bradbrook, sitting in the group's central London headquarters next to a coffin with "Our Future" written on the side.

"That would entail a mass refusal to pay off mortgages and student loans," she said.

"Debt resistance" groups in Britain, the United States and elsewhere argue that refusing to pay debts would spark discussion about alternatives to the global economic system.

Extinction Rebellion wants non-violent civil disobedience to force governments to cut carbon emissions and avert a climate crisis it says will bring starvation and social collapse.

The group is backed by hundreds of researchers and scientists who fear that most people are unaware of the scale of the risks posed by accelerating environmental breakdown.

It is a revolt against the extinction of species including, the group says, our own. It made a "declaration of rebellion" against the British government outside parliament in October.

"I want the system to change so I think you could call that a revolution," said Bradbrook, who graduated top in her year in chemistry at university before doing a molecular biophysics PhD.

With peaceful stunts - such as blocking Oxford Circus and Waterloo Bridge and stopping traffic outside the Bank of England - the group has garnered massive publicity.

Police said 1,130 arrests had been made since the main protests began. A picture of a semi-nude protest in parliament went viral. One activist glued her breasts to the road outside Goldman Sachs European headquarters on Fleet Street.

London police chief Cressida Dick said she had never seen a protest like this during her 36-year career.

Bradbrook said protesters also planned to disrupt other British cities.

LIFE ON EARTH

Extinction Rebellion's headquarters in London look like a grungy version of a tech start-up. Activists with laptops sit at cluttered desks or on run-down furniture amid bags of clothes, boxes of campaign literature and mock skeletons.

Unfurled across a wall is a banner that reads "NO BREXIT ON A DEAD PLANET".

Beneath the apparent chaos is a well-oiled organisation that has inspired copycat actions across Britain and worldwide.

"The big goal - and it sounds crazy - is to save as much life on Earth as possible," Bradbrook said. "So that's not been achieved yet."

The group is inspired by a variety of figures - from Nelson Mandela and India's Vandana Shiva to Vietnamese Buddhist monk Thich Nhat Hanh and Austrian Holocaust survivor Viktor Frankl.

Bradbrook, once "a girly swot par excellence", said Extinction Rebellion was also partly inspired by the clarity she gained taking psychedelic substances including iboga and ayahuasca, both powerful hallucinogens, in Costa Rica in 2016.

The experience, she wrote, "rewired" her brain. She returned to the UK, left her husband and, with a handful of others, founded the movement that became Extinction Rebellion.

The group has been criticised as largely middle-class, but Bradbrook's father worked at a coal mine in northern England.

She lives with her two sons in Stroud, a picturesque town in southwest England with a reputation for new-age activities.

"Everyone is into yoni steaming," she said of a therapy favoured by actor Gwyneth Paltrow involving squatting over herb-infused water. "I've done it once," she laughed.

Asked about the future, however, Bradbrook was more sombre, describing herself as "about as optimistic as a person could be who also understands the science".

"Has it landed with you that your kids probably won't have enough food to eat in a few years' time?" she asked.

She said a climate catastrophe was coming and food security, not civil disobedience, should really be our main priority.

"For every degree of warming you get a one percent collapse in growth. So just do the maths .... We're heading for about four (degrees). That crashes the global economy."

She added, with more hope: "I do have this belief in humanity . . . It's time to stop as a human species and say, 'It's not really working, folks. What else shall we do?'"

(Additional reporting by Matthew Green, Editing by William Maclean)

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