At a secret location near King’s Cross, the London branch of Climate Camp holds its last weekly meeting before the G20 summit.

Sitting on the floor, a young woman cuts bunting from scraps of clothes. A bearded man eats vegetables from a lunchbox. On the whiteboard is a bullet-pointed agenda for next week’s protests. “Take tea and cakes to the ramparts,” reads one item. “Toilet practice,” reads another. The longest says: “Local outreach — visit shops around City to assure them we mean no harm.”

With a £7.2 million policing operation being prepared, Climate Camp, one of the umbrella organisations to emerge from the disparate strands of a decade’s “anti-capitalism” protests, hopes to allay fears that plans to create a vast tent city inside the Square Mile will cause chaos.

But it is one of dozens of protest groups, each with a different idea of what they want from the meeting of the world’s 20 top heads of government. And each has a very different idea of how they want to achieve it.

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Tomorrow hundreds of thousands will take to London’s streets for the “Put People First” march, calling for “the start of a new system that seeks to make the economy work for people and the planet”. The Salvation Army will be there, as will Save the Children and Greenpeace, and the actor Tony Robinson will compere the rally. Anti-capitalism having gone mainstream, this march hopes to be its unobjectionable face, and their demands are moderate enough that most Labour ministers would sign up.

All of which sits uneasily alongside the fiery rhetoric of groups such as G20 Meltdown, which has threatened to hijack Saturday’s event, calling on its supporters to invade any office block with lights on and turn them off to coincide with “Earth Hour”, a worldwide “power down”.

The group, whose public face, the 66-year-old anthropology professor Chris Knight, right, was suspended yesterday from his job at the University of East London after suggesting in a radio interview that bankers could find themselves “hanging from lampposts”, is one of the main forces behind the “Financial Fool’s Day” protests that threaten to cause chaos in the City on April 1, the eve of the G20 summit.

The group appeared yesterday to be distancing itself from the comments that got Professor Knight into trouble. G20 Meltdown said: “We are organising a carnival street-party at the Bank of England on April 1. We are encouraging people to dress up in fancy dress and bring food to share. Comments that have been made by individuals otherwise are misrepresenting what we are organising.”

The group insists that its protest outside the Bank of England will involve nothing more violent than dancing, theatre and possibly a little nudity (“for Emperor’s New Clothes metaphorical purposes”). Mark Barrett, their spokesman, introduces himself to The Times, saying: “I’m with the Government of the Dead and New Sovereignty. Our ideas are about nationalising and decentralising — nationalising everything, and decentralising services so everything is local.”

It is here that the more radical elements are likely to congregate, including anarchist groups familiar from past protests — such as “the Wombles”. Although officially the plan is to create a carnival atmosphere — “Lost your home? Lost your job? Lost your savings or your pension? This party is for you!” they explain — unofficially, Mr Barrett is less certain their camp will remain peaceful. “Revolutionary discipline is not going to happen,” he says. “It would be great for it to be peaceful, a party and fun — and, in terms of taking the public with us — that would make sense.” He adds: “If things are peaceful on the 1st, we will get good press for the 2nd. Then we can ramp it up.”

Meanwhile, Climate Camp will be erecting tents along with — assuming toilet practice goes well — composting conveniences. This is James Holland’s responsibility. “Someone put a call out saying ‘we need toilets’, and I said I’d help,” he explains. “I’ve never done this before. I’ve learnt a lot, though.” His worry is that the police might seize his marquee before he has it set up, testing the modesty of eco-campaigners.

Climate Camp hope to highlight what they see as the impending catastrophe of global warming. Carbon trading is “a crazy system developed by the same people who brought us sub-prime letting”, Kevin Smith, their spokesman, says.

Meanwhile, decorations are a chief concern. “Bunting is the order of the day,” Mr Smith explains. “I’m not sure why, but to fulfil our political objectives, we really need bunting.”

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