The use of supposedly 'green' biodiesel to hit EU renewable energy targets has actually significantly increased greenhouse gas emissions, a new study finds.

By 2020, continued use of biodiesel derived from vegetable oil will increase total EU transport emissions by almost four per cent compared with using its fossil fuel alternative, according to analysis by Transport & Environment, a green group.

That is roughly equivalent to putting an extra 12 million cars to the road, it says.

Countries across Europe have blended small percentages of biofuels into petrol and diesel in recent years in an attempt to cut emissions and to hit the EU's renewable energy directive (RED), which requires 10 per cent of transport energy to come from renewable sources by 2020.