I would agree with sending it to Nikon. I have also read the reviews and so can only assume as there is always some variation between samples yours is unfortunately not the best. I am sure that Nikon UK can correct the fault.
I would suggest setting up some form of test target and enclosing prints that would demonstrate the softness you are experiencing.
I am going through my manual focus lenses that way, as limitations will show up easier on test targets than in a scene. I used a download of the D2X target from DPR camera review.
Pic of my setup attached.
Don
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