The UK's first train to run on biodiesel is going into service as part of an attempt to make rail travel more environmentally friendly.
The Voyager fleet could run on 100% biodiesel in the future
The Virgin Voyager has been modified to run on eco-friendly fuel and the company is aiming to convert more in the future.
The train uses a blended fuel which is 20% biodiesel - to reduce CO2 emissions without harming the engine.
The London-to-Llandudno passenger train left on Thursday morning.
The journey was launched by prime minister-in-waiting Gordon Brown.
Biodiesel is a processed fuel derived from biological sources including rapeseed, soyabean and palm oil.
It is biodegradable and produces less CO2 than conventional diesel.
During a six-month trial, the train will run from Birmingham to Scotland, across South Wales, North East England, the North West, the West Country, the South West and the South coast.
The experiment has been organised by Virgin Trains, the Association of Train Operating Companies and the Rail Safety and Standards Board.
If successful, Virgin hopes to convert its entire Voyager fleet to biodiesel fuel, which could cut emissions by 14%.
Virgin boss Richard Branson said the environmental impact was equivalent to taking 23,000 cars off the road
At the launch, Sir Richard said: "It's fantastic that we are leading the rest of Europe in developing this fuel."
He added that it was bizarre that the tax on clean fuels was higher than on dirty fuels.
"Our indications are from Gordon Brown that he will address this problem. If it is not addressed, we will have dirty fuels and the clean fuels will head abroad to countries such as France and Germany instead."
He said the company hoped in future to use 100% biodiesel - equivalent to removing 100,000 vehicles from the road.
Speaking ahead of the launch, Mr Brown said: "I want Britain to be a world leader in the development and use of environmentally-friendly fuels.
"I believe they will play a fundamental part in our efforts to reduce emissions and tackle climate change."