Tube Lines upgrades and maintains the London Underground's Jubilee, Northern and Piccadilly lines. It employs more than 3,300 staff and in 2008 turned over £874m.
The company's environmental policy has 'more sustainable use of resources' as a major goal, and better management of water has been a key focus in the past few years.
The Green Business Awards judges were particularly impressed by Tube Lines' installation of rainwater harvesting to supply water for train-washing at its Cockfosters depot, cutting the consumption of purified mains water. This was the first application of rainwater harvesting on a major transport site in the UK, according to Tube Lines, which saw benefits not only in reduced mains water consumption but also in a lower carbon footprint. It's now looking at implementing a similar scheme at a separate depot.