The contracts are intended to be the first of a wide-ranging programme to cut carbon emissions across thousands of offices, transport buildings, police stations, hospitals and schools in the capital, making energy savings of up to 25%.

London is the first city in the world to have completed the municipal tender process and appointed a company following a deal developed by the Clinton Climate Initiative for the C40 group of cities at the New York Large Cities Climate Summit in May 2007. Livingstone will also be working with the Clinton Climate Initiative to sign up private sector businesses to make their buildings green.

Honeywell and Dalkia will begin auditing 42 properties next month, including those owned by the Metropolitan Police Authority, Transport for London and police and fire stations, to assess possible carbon savings.

Under the scheme, they will guarantee a set level of energy savings for the GLA's buildings and "retrofit" all 42 with a range of technologies to lower their CO2 output - everything from low energy lightbulbs to new heating and cooling systems.

The scheme will provide discounted goods and services, which will be paid for through the energy savings.

Ken Livingstone said:
"As nearly three quarters of damaging carbon emissions come from energy use in buildings, improving energy efficiency is probably the single most important thing that we can do to cut carbon emissions.

"The Greater London Authority Group is taking the lead, but we want all London's public buildings to benefit from this programme. That is why I will now ask my officers to plan the creation of a Low Carbon Building Unit, to provided on-going support to other public authorities. One million tonnes of carbon emissions, and millions of pounds, could be saved each year if London's municipal buildings and schools, universities and hospitals were to do this.

"If commercial building owners will also join us, these carbon emission savings could rise to 3.6 million tonnes each year - about eight per cent of the capital's total emissions. That is why I am delighted that Canary Wharf has announced their support for this programme and will start the ball rolling with some of their iconic buildings."