The Renewable Transport Fuel Obligation (RTFO), which mandates 5% of all transport fuel in the UK to come from biofuels by 2010, comes into force tomorrow.

As Oxfam has pointed out, this comes just days after Gordon Brown wrote to the Japanese Prime Minister, warning of the potential negative effects of biofuels, and urging him to put food prices on the agenda at the G8 summit in Hokkaido in July.

In February, UK Transport Secretary Ruth Kelly announced a review by the Renewable Fuels Agency (which was set up by the government to implement the RTFO), to examine the indirect impacts of biofuels production. This begins with a "call for evidence" which ends today, with an initial report expected in June.

Oxfam has welcomed the review, but voiced a number of concerns, including the short period provided to third parties in which to provide evidence, the omission of important impacts such as the displacement of people, and the fact that the RFA is conducting the review itself. Oxfam is urging Gordon Brown to delay UK biofuels targets, and push back on EC proposals, until a thorough and independent investigation into the impact of biofuels on climate change and the environment is completed.

There's an timely head to head discussion on biofuels between Ruth Kelly and Peter Ainsworth, the shadow environment, food, and rural affairs secretary, in today's Guardian.