Guardian: Controversial plans to make cars greener by using fuel made from crops and animal fat will be thrown into doubt this week when MPs are expected to question whether they will do more harm than good. Biofuels have been hailed as a green alternative to oil by some, but in the US, where there are massive plants converting maize (corn), it has been criticised for making food more expensive and being environmentally unfriendly. From April, petrol and diesel sold in the UK must have …