aN INVESTIGaTION has been launched into a flagship government emissions monitoring system after revelations that Britain's biggest firms are by-passing it.  The Department of Energy and Climate Change set up its Quality assurance Scheme for Carbon Offsetting two years ago to guarantee the quality of carbon credits used by companies to offset their greenhouse gas emissions.  The move followed complaints about so-called carbon cowboys who were accused of generating the credits by unsustainable or underhand means.  However, new research has shown FTSE 100 companies are shunning the governmentbacked scheme in favour of cheaper options with lighter regulation.  Only 0.4% of the carbon offsets bought by FTSE 100 firms complied with the monitoring system, according to a report by Carbon Retirement, one of the offsetting companies working with the government.  The Department of Energy said there would be a review of the low number of firms taking up the programme and the potential implications of this.  The Quality assurance Scheme is not being widely used because the criteria are particularly robus