The Airport Carbon Accreditation Scheme (ACAS) is the European standard for CO2 management and Heathrow's success will be a major boost to government plans to improve international links and meet strict EU environmental targets.

Heathrow has invested millions of pounds in more eco-friendly air-conditioning to keep people cool and lighting systems that dim down when areas are unoccupied. Like Terminal 5, the new £2 billion state of the art Terminal 2 will also maximise natural light, meaning customers get a brighter experience with great views of the planes at no environmental cost.

Smart metering has also been implemented across the airport to allow Heathrow to manage usage in energy hungry baggage systems. While Heathrow cannot control emissions from planes flying, aircraft taxi times have been cut by 30 percent - helping reduce the length of time engines are powered up while on the ground.

During the last year 131,000 tonnes of CO2 has been saved which is the same as cutting the carbon footprint of 13,000 people to zero.

The ACAS rates Heathrow at Level 3 'optimisation' - the highest level of performance achievable without offsetting emissions.

Heathrow's success has come through three years of joint working across the airport, with airlines, air traffic control, baggage handlers and other ground staff focusing on:

1. improving energy efficiency, cutting energy use and waste
2. greening the energy supply through biomass and combined heat and power plant
3. steps to cut CO2 from passenger and staff travel to the airport, such as the implementation of a clean vehicle scheme to emit less pollution

And with more than six million passengers each month, huge savings have been made by using hybrid vehicles for onsite transport while the airport's 77,000 employees use Europe's biggest car-share scheme to get to work, saving over 19 million miles of travel.

Colin Matthews, chief executive of BAA, said: "If you do not effectively measure and benchmark energy use, you cannot reduce it, but that is exactly what we are doing. This accreditation is an important milestone as we seek to make every journey better. Real improvements can be made through investment and joint-working. We are committed to helping the country meet its environmental targets and I am delighted that the great lengths that all our staff go to have been recognised."