They hoped for ten thousand but in the end more than three times that number turned out on London's streets today for the biggest mass demonstration since the beginning of the economic crisis.

The Put People First march was organised by a "rainbow alliance" of 150 trade unions, church groups and charities including ActionAid, Save the Children and Friends of the Earth. The theme was "jobs, justice and climate" and the message was aimed at the world leaders who will be gathering for the G20 summit here next week.

One of the organisers, the TUC general secretary, Brendan Barber, claimed there had never before been such a wide coalition brought together with a direct message for world leaders. "The old ideas of unregulated free markets do not work, and have brought the world's economy to near-collapse, failed to fight poverty and have done far too little to move to a low-carbon economy," he said. "Of course, the G20 will not solve everything in a day's work, but leaders must sign up to boost the world economy and govern it better, and show us that they are trying to build a better world."

The marchers, estimated at 35,000 by police, accompanied by brass bands and drummers and a colourful assortment of banners and flags, walked the four miles from Embankment to Hyde Park, where speeches from comedian Mark Thomas and environment campaigner Tony Juniper and music from the Kooks marked a party-like atmosphere despite chilly temperatures.

People had come from all over the country to protest; organic farmer Jyoti Fernandes travelled from Somerset with her four children. "We are here to remind people that we have to look after our land and look after our food," she said.

A group about 200 anarchists joined the march but were kept isolated and surrounded by police throughout. Chants of "burn the bankers!" were the closest anyone came to any show of aggression. A few buildings along the route of the protest, such as the Ritz Hotel, had their windows boarded over, but calm prevailed.

Thomas said he believed the protest marked "the start of a grassroots movement".

"This is a moment," he said. "This is the first time people have had a chance to come out on to the streets in a big way."

Kevin Stevens, 43, who had ignored police warnings for City workers to keep a low profile, came dressed as banker in a pinstripe suit . "I thought I might prove all the talk about attacking city workers is nonsense," he said.

Chris Knight, the anthropology professor who was suspended from the University of East London this week for suggesting bankers might be lynched, was wandering the march alone. "I just met a copper and I said to him: is this the revolution? He is said 'no, this is the dry run, the revolution starts on Wednesday. Midweek is when we will really start to dance."

Claire Melamed of ActionAid said the organisers were delighted with the turnout. "We're really pleased. As a development organisation, we are hearing every day about people losing jobs and not being able to feed their children as this economic crisis depends. We want the G20 to listen to us - this began as a financial crisis and its turning into a humanitarian one. Let's not forget the world's poorest next week."

Former Labour party national executive committee member, the TV presenter Tony Robinson, who was on the march and was scheduled to speak at the Hyde Park rally, told reporters: "Like 97% of the people here, I'm absolutely hacked off with what's happened in my country and internationally."

He said the march would have to mark the start of a more concerted movement to properly regulate financial institutions and invest in climate change solutions. "This is just the beginning of the prelude of the prologue. The forces of greed are very tenacious and just because we march up and down it won't make a difference on its own."

Another protester, the general secretary of the Unite union, Derek Simpson, said: "This is about getting across the message that our members give to us about their concern over jobs and houses and the state of the economy. I think it's an important message but whether it will get through to the people meeting in London I don't know. Anyone who sees the numbers on this march should realise how important it is."

Italian trade unionist Nicoli Nicolosi said he had travelled from Rome to take part in today's protest. "We are here to try and make a better world and protest against the G20."

Several thousand police officers were on duty to keep the peace. Organisers had expressed concern that police were spreading stories that the demonstrations would be overtaken by violent anarchists.

Earlier in the day, Barber told the BBC Radio 4 Today programme he was committed to purely peaceful protest. "If there are other groups who want to cause trouble, I don't want to see them anywhere near our event. I read about other events being planned by other groups over the next couple of days. If people want to make their protest in other ways, not the peaceful ways that we are absolutely committed to, then they should go in other directions."

Environmental campaigners are also involved in the protests. The Climate Camp organisers, who had previously staked out Heathrow airport and Kingsnorth power station to protest against the rise in carbon emissions, plan to focus on financial institutions in the City this week. Hundreds of campaigners are expected at the European Climate Exchange with bunting and baked goods. Their aim is to raise parallels between the current economic crisis and the problems of climate change.

Other groups include the Stop The War Coalition and CND, who are organising a rally at the US embassy in London on Wednesday, as well as a protesting at the G20 summit the following day. G20 Meltdown is a new organisation with the aim of organising a party, led by four horsemen of the apocalypse, at the Bank of England on Wednesday, which has been dubbed Fossil Fools Day by Rising Tide, a network of groups that wants to take local action against climate change.

Social networking sites have been used by many marchers to keep each other updated on the progress through the day. On PPF's Twitter feed this morning, the organisers dished out the latest travel hold-ups for those heading to central London and wished their protesters luck. "Try to get there a little early if you can," it said.

"Hail has begun to fall," said BenLaMothe later in the day as the weather worsened. "World Revolution by June," wrote ocicat_bengals optimistically.