Britain's Prime Minister Gordon Brown (L) greets U.N. Secretary-General Ban Ki-moon upon his arrival at the G20 summit at the ExCel centre, in east London April 2, 2009. World leaders are set to declare an end to unfettered capitalism at a G20 summit on Thursday after France and Germany demanded they act fast on promises to prevent a repeat of the worst economic crisis since the 1930s. [Agencies]