SOME of Britain's worst polluters will tomorrow meet Greg Barker, the energy minister, to press their case for a ?2 billion exemption from green taxes they say will force tens of thousands of manufacturing jobs overseas.  The meeting of the Energy Intensive Industries all-Party Parliamentary Group is part of a last-ditch effort by firms who say the government's climate change policies are in danger of strangling an already struggling sector.  Big energy users - steel makers, chemicals groups and cement companies - are most worried about the carbon floor price, a Britain-only emissions tax that comes on top of the carbon permits polluters must buy for each tonne of carbon dioxide they emit.  Civitas, the think tank, said that imposing it amounted to "economic suicide".  The cost of the coalition's green policies has led to a bitter dispute between Chris Huhne, the energy secretary, who is pushing ahead with the reforms, and chancellor George Osborne, who warned against, "saving the planet by putting our country out of business".  Some of the country's biggest employers, including Tata Steel and Ineos, the chemicals giant, have written to David Cameron, asking for an exemption from the carbon floor price and other allowances. This would amount to up to ?300m a year from 2013, when the new tax takes effect, until 2020 when the current targets end, said Jeremy Nicholson, head of the Energy Intensive Users Group.  Nicholson recently led a delegation, including the energy minister Barker, to Germany to highlight the measures the German government has taken to protect manufacturers.  He said: "In Germany green subsidies amount to about (EURO)35 a megawatt hour. Big energy users pay only 50 cents." He hopes Britain will replicate the system, which he said would apply at most to a "few dozen" firms.  Osborne has promised to announce mitigating measures in his autumn statement on November 29.