Of the so-called "Big Six", only British Gas has fully launched a national green deal programme. Under the green deal, homeowners can take out loans to pay for energy efficiency measures, such as solid wall insulation, paying them off through additions to electricity bills over up to 25 years.

The revelation of the slow start from energy companies – which were expected to be the main providers of the deal - comes as the Department of Energy and Climate Change braces for new figures to be published on Thursday that will offer the first snapshot of how the policy is faring in practice. But the data is expected to show that only a small number of deals have been taken up, though more people are signing up for home assessments.

RWE npower told the Guardian that getting the IT systems in place to cope with the additions to bills had proved more complex than first thought, for many suppliers. EDF said it was "registering interest" from customers, but was not yet in a position to offer a deal while it performed further checks on its systems. Scottish and Southern Energy said: "We have had the processing systems for the green deal in place since the scheme launched. However, we are still finalising our own green deal offer and expect to launch it in the autumn." Other companies did not reply to requests for comment.

The Green Deal Finance Company, which will oversee the loans, said that only one of the big six was yet offering a national programme, one was working through an alternative supplier, three were "on the way" to offering deals, and one had not engaged at all with the plans.

Concerns surrounding the policy have prompted a group of construction companies, led by the Green Building Council, to write to Ed Davey, the energy and climate secretary, energy minister Greg Barker and shadow energy secretary Luciana Berger, asking for a cross-party consensus to salvage and improve the green deal. They also urge strengthening measures, such as a discount on stamp duty or council tax for households taking up green deal offers.

The struggles of energy suppliers to offer deals is the latest in a string of delays and setbacks that have beset the green deal, under which households can apply for loans to make their homes more energy efficient, with improvements such as cavity wall insulation and better glazing.

Barker, the Conservative energy minister, said the problems were being rectified – for instance, issues with drawing up the legal agreements necessary for suppliers to offer financial services through the Green Deal Finance Company were being ironed out.

He said: "The companies want to get it right first time when they offer to customers, and that's the right thing to do."

Barker was optimistic about the prospects for the deal. "It may be a slightly slow start but it is early days. There is a job to do raising consumer awareness. When people see what solid wall insulation looks like and see how it improves the look of the home, and the bills, I think that makes a big difference."

He pointed to a part of the policy, called the energy company obligation (ECO), by which energy companies improvements such as new boilers, primarily for low-income households, and that can be taken up by local authorities to fund swathes of their housing stock. "ECO is performing very strongly," he said.

But he also suggested that the government would be willing to bring in new regulations to ensure homes were properly insulated. "We want to see how the market develops, but we could anticipate that at a future date there will be a role for regulation."

Some in the construction industry – which expected to benefit from the need for home improvements – are growing impatient with the green deal policy, which was more than two years in the making. In their letter to Davey, seen by the Guardian, companies including Barratt Developments, Carillion and St Gobain, warned the green deal might not be up to the "monumental task" of refitting the UK's 26m homes. They said the high rates of interest on green deal loans – of about 7 to 8% – were "in danger of acting as a major disincentive" and urged the government to bring in new incentives through stamp duty discounts and regulations that would mean homeowners carrying out major building works would also have to improve energy efficiency.

Paul King, chief executive of the Green Building Council, said: "This is not about judging the green deal too soon, as it is still very young. We need to see what can be done to give it the shot in the arm it needs. I don't see any alternative out there – this is the only game in town, and it's about trying to make it work." He said all parties should be concerned: "Somebody has to pay to retrofit these homes, the government is not going to have the money to pay for that, and the vast majority of people do not have this money sitting in their bank accounts waiting to be spent on insulation."

He said one measure the government could take urgently was to stop landlords renting out buildings with the lowest energy efficiency ratings. There is already legislation in place to give ministers these powers.