Originally Posted by MEGA
High "rated" diesel is a marketing product to sap more profit from the consumer.
Originally Posted by BP website
With its higher cetane quality and outstanding cleaning properties, new BP Ultimate Diesel helps your engine perform better.
Our best-ever diesel is designed to work well in all diesel engines and especially the latest ones with sophisticated fuel injection systems.
Cetane is the key measure of diesel fuel combustion quality. It relates to ignition delay - the time between fuel injection and combustion. Good quality combustion occurs with rapid ignition, and then smooth, complete fuel burn.
With a cetane number of 55 minimum, significantly higher than normal, BP Ultimate Diesel burns more smoothly and completely than ordinary fuel. So it releases energy more efficiently, which contributes to better engine performance
Have a look yourself : http://www.bp.com/retail/ultimateart...tentId=7067699
But if you are lucky enough to not notice the difference. Keep using the cheaper Diesel.