Alameda Park is Mexico City's languid space for lovers and open-air ballroom dancers, the gentlemen in two-tone shoes, the ladies in finery and heels. The cobbled paths undulate from the great earthquake of 1985. You imagine the fairground sinking into the cobwebs of cracks, its Edwardian organ playing forlornly. Two small churches nearby totter precariously. The surreal is Mexico's façade.

Hidden behind the poplars is the museum where Diego Riviera's mural Dream of a Sunday Afternoon in Alameda Park occupies the entire ground floor. You sink into sofa chairs and journey for an hour across his masterpiece. More than 45 feet long and 13 feet high, it presents political and artistic warriors of Mexico past, from the conquistador Hernando Cortés to Rivera himself, depicted as a child holding the hand of a fashionably dressed skeleton, the iconic symbol of the Day of the Dead. Standing maternally beside him is his wife Frida Kahlo, Mexico's artistic heroine. Around them parade the impervious rich and unrequited poor.

Los indignados

What is it about Mexico that is a universal political dream? As in a Rivera mural, nothing is held back: no class martyrdom, no colonial tragedy. The message is freedom next time.

The autocracy that emerged from the revoution of 1910-20 gave itself the Orwellian name Party of the Institutionalised Revolution. This was eventually replaced by businessmen promising a pseudo-democracy, which in 1994 embraced Bill Clinton's rapacious North American Free Trade Agreement (Nafta). Within a year, a million jobs were destroyed south of the border, along with Emiliano Zapata's revolutionary triumph, the constitutional protection of indigenous land from sale or privatisation. At a stroke, Mexico surrendered its economy to Wall Street.

The beneficiaries of the new, privatised Mexico are those such as Carlos Slim, now the world's richest man, ahead even of Bill Gates, and whose fingers are lodged in every imagi­nable pie, from food and construction to the national telephone company. A US diplomatic cable released by WikiLeaks says: "The net worth of the ten richest people of Mexico - a country where more than 40 per cent of the population lives in poverty - represents roughly 10 per cent of the gross domestic product."

The last presidential election, in 2006, was won by Felipe Calderón, Washington's man, following persistent allegations that it had been rigged. Calderón declared what he calls "a war on drug gangs" and 50,000 dead are the result. No one doubts the menace of the drug cartels, but the real "security issue" is more likely the resistance of ordinary Mexicans to an enduring inequity and a rotten elite.

For most of this year, thousands of los indignados have taken over the huge parade ground known as the Zócalo, facing the National Palace. The occupations in Wall Street and London and around the world have their genesis in Latin America. The difference here is that there is none of the angst about the protesters' "focus". As in all places where people live on the edge and the state and its cronyism cast lawless shadows, they know exactly what they want. Ask some of the 44,000 employees of the national power company, who prevented the fire sale of the national grid until Calderón sacked them all; the striking copper miners of Cananea, whose owners funded Calderón's campaign; and the former pilots and stewards of the national airline, Mexicana, dissolved in a sham bankruptcy that was a gift to the private airline industry.

These angry, eloquent and often courageous people have long known something many in Europe and the United States are only beginning to realise: there is no choice but to fight the economic extremism unleashed in Washington and London a generation ago. Employment, trade unionism, public health, education, "life itself", says Manuel López Obrador, the former mayor of Mexico City who ran against Calderón, have "since been struck by a political and economic earthquake". Since Cal­derón came to power, 30 journalists have been killed, 13 this year alone, according to the United Nations. Again, the government blames the drug cartels, but suppression of a national resistance, co-ordinated with the United States, is also the truth.

Green-eyed disdain

Unlike in the US and Britain, many journalists, some of them inspired by the rise of the Zapatistas in the 1990s, have thrown off the patronage of the political and business elite to pursue what they call "civic journalism". The second-largest newspaper in Mexico is La Jornada, famed for its fearless investigations and campaigns and for surviving mostly on subscriptions. It carries no commercial advertising, reminiscent of newspapers before they were consumed by corporations. There is nothing like it in Britain; it reflects much about Mexico City that is surprising and enlightened.

At the National Palace the presence of Robocop guards is at once overwhelmed by Rivera's greatest mural. Painted between 1929 and 1945, it follows the walls of the staircase, spilling, like his Alameda work, spectacles of revolution and tragedy, hope and defiance. When I filmed it 30 years ago, I tried unsuccessfully to write a narrative to the pictures. Condensing and bringing alive 2,000 years of history is art of which Europeans and North Americans are sometimes disdainful yet envious; because it charts the struggle of ordinary people, uniting and celebrating them, and identifying their true political enemies. Seeing it again, I am struck by how it speaks for us all.

On 1 November, John Pilger was awarded Britain's highest honour for documentary film-making by the Grierson Trust in memory of the documentary pioneer John Grierson.