Containing the bare minimum of additives and low cetane rating I prefer not to use supermarket fuels as they are of very low quality compared to the main brands like BP and Shell.
However, if I am forced to use it due to running low on fuel and the nearest fuel station is Tesco's for example, I add 100ml of 2-EHN (99.5%+ pure high performance Cetane booster.
http://www.trinity-research.co.uk/pr...products_id=49) to every 25l of diesel. This increases the fuels Cetane rating to a level my car appreciates and 25l is more than enough to get me to a branded fuel station like Esso, Shell or BP.