Apparently the supermarket & brand fuel is the same stuff, only difference is additives.
Try some diesel additive, you'll see instant MPG increase- however, the cost of the additive outweighs the benefit in MPG. That's all "superfuel" is, normal fuel with additive. 
Wynnes DPF cleaner gives a very good MPG increase & slight increased response too- pretty pointless though.
this was a comment attached to an 'Honest John' topic regarding the difference between supermarket and branded fuels a few years ago;
"Use Shell.
Much higher cetane rating which means the fuel ignites easier. When a fuel is essentially more flamible it burns more completely. As oppossed to a supermarket fuel which has no/low amounts of cetane booster (2-EthylHexylNitrate) which has a lower cetane rating, UK spec 51.
When our diesel cars re-circulate exhaust gasses, NOX, this burns cooler in the combustion chamber and the fuel burn's incompletely, forming carbon, soot.
A higher cetane fuel like Shell fuelsave or bp ultimate has a centane of around 56/57. More fuel is therefore ignited at any air/nox mix and leaves less soot.
I'm sure you are aware, carbon in the internals will eventually lead to component failure, the first stop, DPF"
So where does red diesel fit into this picture? Is it the same fuel with additives (colourant) that makes the diesel burn with so much soot. Why do Webasto heaters love a clean burning (branded) road diesel as opposed to red diesel which soots up the internals and creates premature internal component failure?