The obligation came into force on 1 September 2009 and ran until 31 December 2012.
[3] The programme delivered carbon savings of 16.31 million tons of CO2, 84.7% of the target.
Progress was slow at first, and the majority of the savings were only achieved in the final six months of the three-year programme.
Meanwhile, British Gas, SSE and Scottish Power fell short, leaving Ofgem considering whether to impose a financial penalty.
Four independent generators were also set targets, with which only Eggborough Power complied.