Launching this month, the Green Deal allows householders to take out a loan with companies who undertake work such as upgrading old boilers and lagging lofts, with the repayments theoretically offset by energy savings.
But a Guardian newspaper survey of the 24 companies listed as domestic "assessors" for the scheme found that, of the 18 that were contactable, five will charge between £95 and £150 for an upfront assessment fee. Eleven were not able to answer the question, one (Mark Group) plans to offer the assessment for free.
The shadow climate change minister, Luciana Berger MP, said: "In order to be a success the green deal has to be a good deal for the public. It's unlikely that most people will think that paying £100 before they can even decide if they want to take out a green deal package is worth doing. Charging such a high fee is likely to deter those on low incomes and pensioners - exactly the people who could benefit most from installing energy efficiency measures."
The government is phasing out its existing Warm Front and Carbon Emission Reduction Target schemes - in which loft insulation and energy-saving lightbulbs were given to householders for free to cut energy bills and emissions - in favour of the green deal and the Energy Company Obligation, which is targeted at lower-income households. In November, it was revealed that not a single household in the UK was on the central register for the green deal, despite assessors being able to go into homes from 1 October.
British Gas is the only big-name company currently listed as offering assessments, and it will charge £99 for its experts to go into homes and judge what measures, such as fitting cavity wall insulation, would be most appropriate for each property. Two of the companies contacted by the Guardian said they would refund the full assessment fee, or part of it, if works were also carried out with them.
Ms Berger added: "When Labour raised the cost of assessments with ministers during debates on the energy bill last year, they told us they expected companies would not charge customers for assessments. It's now clear they were wrong and their mistake could seriously lower green deal take up. DECC needs to look urgently at what action it can take to reduce the cost of assessments for those who are interested in taking out the green deal."
A DECCspokesman said: "Far from being put off, the green deal customer is in charge. It is a competitive market and we expect to see a variety of different offers allowing people to shop around for the one that suits them and their budget. As green deal plans become available in January, it is likely that some providers will offer free assessments as a way to attract customers while others may charge for it initially and reimburse it as part of a green deal. And there's separate support for low income households, who can benefit from mandated help from their energy supplier without a green deal assessment."