Hi Everyone.
Many thanks to everyone for all the replies.
To be honest.... it's not the start to the D750 I wanted.
I contacted Nikon yesterday via live chat. The chap there confirmed all D750's should have the sticker with the serial number on them on the bottom of the camera. He also confirmed no Nikon camera would leave the factory without this on. He was very interested to find out where it came from, and also guessed it was a grey import. He was totally confused how this could happen - the only thing he could say was maybe the grey importer took the sticker off.... but he said they dont normally do this - they just take the warranty card out the box normally.
So then I contacted HDEW... they were very shocked.... they couldnt understand it and requested the camera back so they could investigate it. They offered a full refund or a straight exchange. They assured me they only sell geniune products and seemed concerned about this incident.
So I cant fault their handling of this.
I will be honest, it's made me nervous.... I dont want a camera without the serial number (in case I ever want to sell it), and maybe it's my over active mind... but i started stressing that it was a counterfiet.
However, I've opted for an exchange from HDEW.... hope i've done the right thing.
I'll let you all know how this pans out
Once again thanks for the input