Ed Miliband's hopes of having a key government policy on renewable energy in place before the Copenhagen summit have been dashed by internal wrangling over the final levels at which so-called “feed-in tariffs” (FITs) will be set. Officials at Miliband's Department of Energy and Climate Change (DECC) have admitted that the announcement – originally due around now – will not come until January.

The Treasury insists the full details of the FITs are still scheduled to be released around the time of Alistair Darling's pre-budget report on 9 December. But sources say Treasury officials – egged on by the regulator Ofgem – are having last-minute concerns about the potential cost.

Energy companies, in turn, are worried that the delay will jeopardise the supposed 1 April launch date to FITs consumers, because they may not have had enough time to prepare for it. The nuclear industry, too, has been lobbying against support for renewables because it undermines the case for new nuclear stations.

FITs work by rewarding installers of renewable energy sources, such as wind turbines or solar photovoltaic panels, for every unit of green electricity they generate and/or feed in to the national grid. They produce a steady return on investment for households, thus stimulating take-up of renewables and the growth of a new industry. Germany introduced one a decade ago and has created more than a quarter of a million jobs as a result.