Leaders of the world’s biggest economies and developing nations are negotiating at the G20 summit in London on how to beat the global economic crisis.Behind the smiles as they gathered for the pre-meeting family photo, there was some tension with different ideas on priorities. US President Barack Omaba has said he is confident differences can be overcome and the world’s political leaders will reach an “unprecedented” agreement on responding to the global financial crisis. However, the German Chancellor Angela Merkel and French President Nicolas Sarkozy have warned they will not sign up to the summit communique unless it contains concrete announcements – not just promises – on tougher regulation of financial markets. Sarkozy has denied that his hardline stance is “grandstanding” for a domestic audience. Merkel said: “This is an historic opportunity afforded us to give capitalism a conscience, because capitalism has lost its conscience and we have to seize this opportunity.” Spanish Prime Minister Jose Luis Rodriguez Zapatero is attending. Although Spain is not part of the G20, its tough banking laws are credited with helping minimise the effects of the financial crisis there. Russia President Dmitry Medvedev is also a key participant; Russia’s economy has been seriously weakened by slumping oil prices. As the leaders met, world share prices – battered by the crisis for months – are starting to recover. But analysts are sceptical as to whether the summit communique will generate much more market optimism. The gathering brings together the world’s biggest economies, developed and up-and-coming. The 20 countries account for more than 80 percent of world trade and economic output.