[gubby]

For some types of power supply, not having a proper ground can dangerous for reasons many people don’t realise. It’s not just about fault currents ‘flowing to ground’. Should just the supply neutral become disconnected, such as during high wind, then without a proper ground setup every metal item in your house that is grounded (such as microwave cases) can become live. It depends on how things are configured, but this type of lethal fault is a real possibility if neutral and ground are bonded at your house as they often are.

In the case where your power is derived from another property as you describe, in the UK we would normally call this a ‘TT’ power supply which you can google. It is absolutely essential (life and death) to have both a good grounding rod and an RCD at your end.

A others have said, get an electrician who understands the subtleties of outbuilding power supplies. If you cannot do that for whatever reason, I suggest first reading up extensively on the different kinds of earthing system, and finding out which one you effectively have.

Since you had no ground previously, it is likely that just live and neutral have been exported from your neighbours property (TT). You can probably check this by visual inspection, and it isn’t actually a problem provided you fix the grounding and protection at your end. To fix this grounding problem what happened? Did the electrician install a grounding rod? Did they happen to measure the impedance of it and write that somewhere? Do you have an RCD in your consumer unit (fuse box)?