Because I've never been in this situation before.
We've been tidying up the garden and have piles of rubble all over the place. One of our rickety old fences borders a graveyard (very old belonging to ancient church) and I'm assuming the skull sort of drifted under our fence and has been near the top of the soil for a while. I hope.
I've googled but can't seem to find much info. I'll be contacting the parish council on Monday but wondered if it warrants a call to 101 (or whatever it is) to register it just in case it's not a graveyard wanderer 
Anyone had a similar experience?!