 The world's biggest greenhouse gas emitters, China, the US and India, will be legally bound for the first time to cut their emissions in a new international climate change treaty to be signed by 2015 and to come into force by 2020.  The "Big Three" polluters finally agreed to a legal regime of emissions cutting at the close of the UN Climate Conference in Durban, South africa, at 5am yesterday morning, after most observers had thought deadlock was certain. The conference outcome is a substantial achievement for the European Union, which had proposed the new treaty and wanted, and obtained, a "road map" towards it.  Chris Huhne, the Liberal Democrat Energy and Climate Change Secretary, who led the British team at the talks, said pointedly last night: "This is a very good example of how the European Union can act crucially in the British national interest, in a way we could not possibly achieve on our own."  The deal was finally clinched in a face-to-face talk between two women negotiators - the EU's Connie Hedegaard, and India's Jayanthi Natarajan.