Just found a place near Southampton who sells proper biodiesel for £1.13/litre. Just got a full tank of it and running it straight in my Transit. Runs great! Until now I've been running a mix of diesel and new veg oil which worked fine.
I don't know exactly where it comes from. Guy I bought it from buys by the 1000L container from a company in Kent who manufactures biodiesel in bulk from waste vegetable oil. Apparently one of the Universities is involved with designing and testing it. Definitely 100% biodiesel!