Campaigning journalist George Monbiot used a War on Want event to call for direct action against Benn's Department for International Development for its support of privatisation of public services in developing countries.
Monbiot said he was "weeping with rage" at DfID's policy of using aid money to fund UK consultants such as Pricewaterhousecoopers and the Adam Smith Institute to advise third-world governments on privatising utilities, which was exposed in a recent War on Want report.
He said he had just returned from South Africa where the city council in Johannesburg had installed water meters in township homes as part of a privatisation scheme. 200 people, unable to afford the charges, subsequently died from cholera after drinking water from a local river.
Monbiot said the issue was "as big as the Iraq war" and called for ministers to be subject to non-violent, direct action and shouted down at meetings if they attempted to justify their policy.
The journalist's fiery speech was greeted by a standing ovation that included War on Want's chief executive Louise Richards, impeccably attired in a Guevera beret.
The Forum, a gathering of social movements, saw mainstream UK NGOs such as Amnesty and Friends of the Earth rubbing shoulders with Marxist Leninists from Kurdistan at London's Alexandra Palace.
Perhaps stung by a report last spring that claimed that young activists regard them as snobbish and conservative, NGOs were out in force, fronted by young, T-shirted volunteers and addressing seminars on corporate power and international trade rules.
But none came close to the revolutionary chic of the youth wing of the Italian communists, selling cups of espresso alongside Che Guevera T-shirts.