At 1/4 ohm sounds like TN-S - I presume you looked and found no clip or soldered tail on the lead cable though, so it is acting as underground TT.
Mind you, acting as an electrode the gas and water pipes or the metal jacket of the cable coming in will all leave you pretty well coupled to the substation earthing, what ever you try to do with a short bit of metal in the garden in parallel. That may be what you are measuring really, if there is no formal electrode.
At 1/4 ohm sounds like TN-S - I presume you looked and found no clip or soldered tail on the lead cable though, so it is acting as underground TT.
Mind you, acting as an electrode the gas and water pipes or the metal jacket of the cable coming in will all leave you pretty well coupled to the substation earthing, what ever you try to do with a short bit of metal in the garden in parallel. That may be what you are measuring really, if there is no formal electrode.
