EDF Energy admitted last night that its power stations were pumping out more carbon dioxide than in previous years as it cranked up output from its coal-fired generators.
For every gigawatt-hour of electricity produced, its power stations churned out 251.7 tonnes of CO2 in 2012, a sharp increase from the previous year's 208.1 tonnes. It also marked a change in direction, for the worse, because the 2011 figure had been an improvement on 2010.
EDF's total carbon footprint also increased during the period.
The performance on greenhouse gas emissions meant EDF was behind its stated target of reducing emissions by 60 per cent by 2020.
EDF admitted it had missed its targets for improving its green credentials, but said the situation would improve as it built more nuclear generating capacity. It has said it plans to build four new reactors at Hinkley point in Somerset and Sizewell in Suffolk, although the projects are behind schedule due to concerns over the investment terms. Centrica pulled out of involvement with the Hinkley Point plan after the £14bn project's costs rocketed.
However, EDF's sustainability report claims that it can still meet its 2020 emissions targets even without the new reactors. Extending the life of its existing nuclear plants, where safe, and a new combined cycle gas power station in West Burton, Nottinghamshire, would deliver cleaner energy, along with renewable energy generation on and offshore, it said. A Friends of the Earth spokesman, Guy Shrubsole, said the extent of the increase in emissions was "surprising" but added: "There has been an increase in use of coal in the UK and Europe because of the collapse in the coal price in the US because of shale gas discoveries.
"But it is also because the EU emissions-trading scheme is simply not attributing a high enough cost to carbon."
EDF admitted it had failed to hit its targets on the energy efficiency of its buildings, or getting its staff to participate in and understand its sustainability commitments.
The report also showed a sharp increase in employee sick days, from 119,884 in 2010 to 140,953 last year, and "work-related ill health incidents" from 4.08 per 100,000 hours worked to 5.83.
EDF stressed it had reduced the number of incidents that had led to people taking time off work by 85 per cent in the past five years.