I have recently gained access to the cellar my house hasn’t been seperated and none of the fuse box’s are for my property
Is there a question here?
Follow the power cord, maybe the fuse box was installed in the house (in the hallway in a storage room or in the kitchen in a closet). Or contact the electricity company that sends you the bills.
I would call a electrician in to look at it and inform the neighbours about it
I would be getting in touch with your neighbours and finding out who they belong to, getting them moved and getting a party wall installed