I was running Bio till a few weeks back, got a bit hard to start from frozen one a really cold morning though (could have been due to a somewhat defective battery however), so I since stopped using it.
Never run actual veggie oil on me car, I think I will stick to regular derv though until the summer. 56p a litre in Tesco does sound good, mind you 75p a litre of Bio was pretty darn good too!