A few reverse searches popped up this similar looking doohickey on a Russian utility pole. I think this is part of a tension support.
What is this thing?
Let us help you identify that mysterious object you’ve found.
Currently in CHALLENGE mode: If you've got something obscure knocking about, post a picture, and let's see how we do. Please prefix such posts with "CHALLENGE:" so we know we've got a fighting chance.
1m from the pole seems a bit close. Now, I'm not a lineman so I cannot tell you much but my guess from looking at loads of telegraph poles throughout my existence is that it may be from an older pole that was placed a bit further away from it.
I assume it's one of those things they've forgotten about when they changed poles because it was buried in your garden.
Looks like a turnbuckle to me for tensioning the cable it’s attached to.
You can't pull it out of the ground as it should be attached to the pole you mentioned, it's to stop the thing falling over! No idea who or how you'd report that too... openreach maybe???
If you want to nerd out > https://www.powertelcom.com/guy-wire-function/
Make sure you have a plan of the boundaries of the property as they may well ask questions about the fence and whose land it is on.