The government announced in its energy white paper, published on Monday, that it was aiming to reduce the UK's emission of greenhouse gases by 60% by 2050.
Industry environmental experts said that if this was to be achieved, legislation would be needed to police the energy consumed by existing buildings. So far, the government has concentrated on emissions from new buildings.
Rab Bennetts, founder of architect Bennetts Associates who chaired a government taskforce that devised key performance indicators for sustainability, said environmental policy should not just concentrate on new construction.
He said: "It is easier to get new buildings to perform more efficiently by adjusting legislation. What we need in this country is an energy rating scheme where we can target existing buildings and identify the worst offenders."
Andrew Warren, director of the Association for the Conservation of Energy, said: "Building stock comprises 40% of all energy used in the UK. The government must now focus on increasing energy efficiency in existing buildings, perhaps looking at the grant schemes in the 1970s and 1980s that provided extra money for loft installations."
Warren added that the 60% target was realistic, despite a claim to the contrary by leading environmentalist Jonathon Porritt. Warren said: "The target is achievable. The white paper shows a feeling of urgency in the need to upgrade Britain's buildings in terms of energy performance."
Others in the sector criticised the white paper as lacking detail. A Construction Products Association spokesperson said: "Disappointingly, there are no firm commitments regarding the reduction in VAT for energy-efficient products, which would encourage households to improve efficiency in their homes."
The CPA said it would keep pressing the government to set "strict targets" on within the communities plan, launched last month to solve the housing crisis in England. The CPA will also be working alongside the Office of the Deputy Prime Minister on revisions to the regulations for new buildings, due to come into effect by the end of 2005.