Brown tells demonstrators: I will meet all your concerns

As 35,000 protest in London, and Germans leak alleged G20 paper, Prime Minister takes a gamble

At the start of a week that could determine the economic fate of the planet, as well as his own future, Gordon Brown last night took the gamble of raising expectations for the G20 Summit by pledging it would meet the concerns of protesters demanding fundamental change to haul the world out of recession.

The Prime Minister insisted the landmark gathering in London would respond to unprecedented global demands for action, with measures to "create jobs, stimulate business and get the economy moving".

His pledge came as a broad alliance of activists demonstrated in European capitals including London, where at least 35,000 people took to the streets in a march for "jobs, justice and climate".

The Prime Minister was given a sharp reminder yesterday that the next six days are likely to be a bumpy ride when a German magazine produced a leaked G20 document, which it claimed showed he had put a £1.4trn price tag on rescuing the world from financial meltdown.

Der Spiegel said the confidential "draft communiqué" laid out a $2trn (£1.4trn) package of "stimulus measures" which Mr Brown planned to put before the gathering.

Downing Street dismissed the allegation – claiming the document was "an old draft that has changed in a number of respects" – and insisted that the $2trn stimulus referred to money that had already been committed by world governments.

A No 10 spokesman added: "This is not a new figure. It does not relate to any new commitments and is derived from [International Monetary Fund] figures already in the public domain."

Speaking in Chile at the end of a pre-G20 tour, Mr Brown attempted to defuse tensions over his handling of the economic crisis, claiming he understood the public's worries over their jobs, homes and businesses.

He added: "That is why the action that we want to take is designed to answer the questions that the protesters have raised, and also which the British people have.

"The action that is happening in London today I both understand and we will respond to at the G20 with measures that will help create jobs, stimulate business and get the economy moving."

Mr Brown faces a difficult week reaching agreement with fellow leaders of the 20 most developed and developing nations in the world over the best way to revive the global market from its slump. He is expected to find himself lining up with the US President, Barack Obama, against the German Chancellor, Angela Merkel, and French President, Nicolas Sarkozy, in the argument overusing "fiscal stimuli" – pumping state aid into the economy – to trigger a recovery.

The draft cited by the German magazine includes the pledge: "We are determined to restore growth, resist protectionism and to reform our markets and institutions for the future. We believe that an open world economy, based on the principles of the market, effective regulation and strong global institutions, can ensure sustainable globalisation with rising well-being for all."

The behind-the-scenes political wrangling has taken place against a backdrop of rising tensions over the potential for unrest sparked by protests against those blamed for plunging the world into financial crisis.

A few miles away from the ExCeL centre in London's Docklands, where the world leaders will gather for their meeting on Thursday, thousands of people marched through the capital to register their discontent with the Prime Minister and the senior bankers who have become public enemies over the past few months. At the same time, thousands of police from six forces were drafted in to London to assist the Metropolitan Police. But they kept a relatively low profile as campaigners from across the UK and around the world braved rain showers to take part in the first of a week of demonstrations around the G20 summit.

The huge police operation was launched as officers warned of an "unprecedented" threat posed by the protests. But by early evening as a rally in Hyde Park ended there were no signs of problems, backing up the organisers' earlier pledge that events would not turn violent.

The Metropolitan Police said a single arrest – for drunkenness – had been recorded by 4.40pm. Police estimated the crowds at around 35,000. The demonstration, which was organised by trade unions, aid agencies, religious groups and environmentalists, took place under the slogan "Put People First".