The company manages around 3,000 cars on its internal vehicle fleet and is encouraging drivers to consider the environmental and financial benefits of choosing a cleaner car when the time comes to change their vehicle.

Drivers can take advantage of financial incentives offered by the company in return for downsizing one grade on their new company car. Carillion has also identified specific models that qualify for "Green Star Car" status, meaning the vehicle has the lowest CO2 emissions in its class.

Not only is this helping Carillion to lower its overall fleet emissions, it also means drivers can enjoy lower fuel bills through better fuel economy, plus a reduction in Benefit in Kind tax bills from cutting their vehicle emissions.

Bob Dunnett, managing director of Carillion Fleet Management, said: 'It's all part of our efforts to encourage drivers to think more about the costs of running a car, while still providing a vehicle that fits with our health and safety offering.'

Essential users are offered a choice of Ford or Volkswagen vehicle, with a wider mix for user choosers – but all with the aim of reducing emissions and increasing fuel economy.

Mr Dunnett added: 'Our goal has been to reduce our CO2 emissions by 50% between 2007 and 2012, and we are making good progress towards this. Almost all our vehicles are now below 160g/km but we are actively encouraging drivers to opt for sub 110, 120 and 130g/km vehicles.

'Recent developments in engine technology mean we are able to do this without asking drivers to sacrifice comfort, refinement and equipment.'