I am a phantom 3 flyer in East Sussex uk and i have found a phantom 4 standard. No matter how much i would love it  myself can DGI trace the owner? It has been outside of sometime and the SD card will not read  but the battery has some charge.
I have reported it to the police.

You should charge the battery up before handing it to the police so that when you get it back because it hasn't been claimed, the battery will still be in good condition ;)

While DJI could probably trace the probable owner quite easily, I don't think they will be prepared to do so.   

People who want their lost Phantoms returned should put their name and phone number or email on them before take off, if they don't then they shouldn't expect them back.  Handing it to lost property is the right thing to do, you will quite likely get it back though.

Maybe try putting another thread on P4 forum, also serial number should show who initially activated it.

Good points i will post on phantom 4 forum but keep the SN to myself so the owner can prove it's their one

The best proof of ownership is for them to bring the RC, if they are already paired then it is good proof.

A serial number is not quite so good since it could have been sold on locally so more than one person could know the serial number.