It has nothing to do with the country, diesel is cheaper wholesale now due to increased refining capacity in the middle east.
Long term this could be the case, however give a couple of months and the demand for heating oil starts to effect prices. ie. unl down and dv up.
The difference in the middle east is Saudi's exporting refined products like diesel now instead of just Crude. With the Thames oil port open in the future importing dv will be easier too.