Big six are behind target on measures such as paying for insulation, but are continuing to add cost to bills

The big six energy companies have come under fire again as it was revealed they have taken £1bn from their customers while completing a fraction of the thousands of green and social measures they are required to carry out.

Figures from the regulator Ofgem showed that the companies had achieved as little as 3% of the measures to be carried out under one section of the Energy Companies Obligation (ECO), by which they are supposed to pay for solid and cavity wall insulation, particularly for people on low incomes or with hard-to-insulate properties. Companies had achieved 16% of what they needed to do to help rural areas and put in district heating systems, and 25% of the target on measures that reduce the overall cost of home heating for low-income and vulnerable households, including new boilers.

These figures come as the scheme is more than halfway through, as the full complement of measures must be installed by March 2015. Energy companies want the government to extend the deadline, because on current rates they cannot meet it. But while the companies have made slow progress on their targets, they have carried on adding a charge for ECO to customer bills. This has netted them about £1bn so far, according to separate research by the Local Government Association. By the end of the current ECO period, in March 2015, the energy companies will have collected £1.625bn towards ECO, according to the LGA.

The LGA also calculates that of the £2.1bn that should have been delivered by now in savings on bills to fuel-poor consumers through the insulation measures, only about £1bn of savings are being made. This is leaving tens of thousands of fuel-poor households with cold houses this winter.

Andrew Warren, director of the Association for the Conservation of Energy, said: "They have collected £1bn and spent a small proportion of it. This is cynical price-gouging by the big energy companies. We are discussing social obligations here, not a green tax. These companies are blaming ECO for rising energy bills, but they haven't been carrying out [the number of installations needed]."

The ECO has become the focus of the debate over energy bills, as one of the targets for David Cameron's pledge to "roll back" some of the additions to bills that pay for green and energy efficiency measures. Several energy companies have suggested transferring the ECO, which is currently paid for by them through extra charges to bills, to be paid for from general taxation. But the Treasury is reluctant to find the £1.3bn necessary to fund the scheme, so it could be scaled back or its future thrown into doubt.

Mike Jones, chairman of the LGA's environment and housing board, said: "The ECO is there to give vulnerable people warmer homes which cost less to heat. The energy companies have collected more than £1bn from our fuel bills and we don't think the measures are being rolled out fast enough."

Warren pointed out that the Treasury already gains billions from another so-called green tax, the carbon floor price, by which businesses pay a guaranteed price for their carbon emissions. The floor price has been criticised, however, for not saving carbon because the overall carbon cap is set not by the UK but under the European emissions trading scheme.

Warren said it was wrong to attack measures aimed at helping consumers, particularly those on low incomes. He said: "The big companies are telling lies and lies. These guys are playing games with people's lives, because that's what cold homes mean."

Ofgem will not break down the performance on ECO by individual company until later this year, but in a previous breakdown based on figures this summer, Centrica had achieved less than a tenth of its targets, while Eon was out in front with about three-quarters of its installations achieved.

Angela Knight, chief executive of Energy UK, which represents energy companies, said the charges to cover the ECO had been added to bills in advance in order to avoid "a big bounce" in bills at a future date. She added there had been a slow start to the ECO as there was a hiatus between the end of the old scheme and the start of ECO, and that many companies might have entered into agreement with subcontractors to carry out the work. "Unfortunately, there is no easy option," she said. "You can bounce bills around or you can try to spread the price more evenly. Companies have to spread this over the period."

She said Energy UK did not take a view on whether ECO should be paid for from general taxation, as that was a matter for politicians to decide.

But Warren said the large difference between the best and worst performers suggested these were not the only explanations: "If Eon can do it, why can't the others? EDF have been trying to blackmail the government."

Don Lieper, director of new business at Eon, said: "We take this very seriously – it is a legal requirement. We are very proud of what we have done – it hasn't been easy, but we have been helping vulnerable customers." By the end of August, the company had spent £130m of the projected £400m it expects to spend on ECO.

Npower said it was moving faster on ECO and would be able to report better progress soon. Scottish Power said it had now signed contracts with installers for 70% of its target. Scottish and Southern Energy said: "These Ofgem figures are two months behind the current position. Since then, SSE has significantly ramped up the number of measures completed and we are confident we will achieve delivery by the end of March 2015."