I'm looking for a way to earth in an old 4 story building. At the front of the building is the mains supply in, with meter etc. In the ground under where the meter is situated is a good copper earth rod. A single wire runs up from the rod to a small white plastic box, on which is the tube for the electric bill. From this box, twin core (both black) comes out.

Pictures please.

Yes, we need to see photos, but I suspect it's one of the MEA/PEA grounding points in which case you should not use it (it's their property).

If you can get a wire down to that point it's only a little further to get your own rod in, Forky will let us know how far from the PEA rod this rod should be positioned.

Thanks for the replies. Pictures as requested

The 'small' box in your second picture is a Telephone drop wire station protector (over-voltage arrestor). It and the ground spike are put in by the Telco and are considered part of their equipment.

Yup ^^^, using that rod is a no-no, sorry.

You could put a clamp on that iron water pipe that goes into the ground if you can't get a rod in.

Thanks. Sad for me