Heathrow has received the optimisation accreditation from the Airport Carbon Accreditation.

The award - which it has been given consecutively for four years now - showcases the highest level of performance without offsetting harmful emissions. Heathrow states it is the only certificate endorsed by an independent body available to airports.

Programme director at Sustainable Aviation Dr Andy Jefferson said: "It also recognises the enormous efforts the airport invests in working collaboratively across the aviation industry to reduce its impacts whilst maintaining the significant benefits it provides to passengers and the UK economy."

A number of green transport schemes are present at the hub, including Europe's biggest fleet of electric airside vehicles. It also encourages cleaner fuel with the country's first hydrogen fuelling station with public access.

However, Heathrow has come under attack recently after the Civil Aviation Authority declined to cut the airport's charges - some of the biggest landing charges worldwide. The body did agree to limit further increases relative to inflation.  

Heathrow points out its newly-upgraded Terminal 2, opening next year, has been recognised for reducing energy use. It has a goal of cutting CO2 by 40.2 per cent more than current building regulations.