Outdoor Building Power

[Risteard]

Just run a 10mm three core and bond the metal, far better than messing around with earth rods.

True, but there isn't any harm in additionally installing an earth electrode (as opposed to implementing a TT arrangement).

 

[Risteard]

It is then TN-S inside the property.

It isn't TN-S inside the property. TN-C-S means Terra (Earth)/Neutral Combined and Separate - i.e. combined on the supply side and separate within the installation. If you had a PEN conductor within the installation that would be TN-C (not TN-C-S).