Winter Diesel to BS EN590: 16th Nov to 15th March.
Summer Diesel to BS EN590: 16th March to 15th Nov.
Basically we have just switched over to summer diesel and this will be peoples first fill of summer fuel. From my experience the fuel additives quality and amount plays a big part in fuel performance.
Also, like others have said diesel engines are much more efficient than petrol engines because of the lower wasted energy (heat) losses. Diesels are typically 30-35% more efficient at turning it's fuel into mechanical energy than petrols.