Government plans to make homes more energy efficient could reduce the amount mortgage buyers can lend .
Under new government proposals, homeowners will be allowed to borrow money to cover the up-front cost of eco-upgrades.
Homeowners will be able to take out a long-term loan to help pay the costs of the energy efficient work.
The government, however, has conceded that although efficient homes were less expensive to run, this had not yet impacted on house-buyer demand or property prices .
It said: "A price differential between energy efficient and inefficient homes, coupled with the added prospects of lower fuel bills, would offer homeowners greater incentive to invest in energy efficiency measures."
Energy efficiency refers to using less power to provide the same level of service.
The International Energy Agency has claimed energy efficient buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third.
