On earthing conductor size for TT....
See table 4.2, page 29 in the latest OSG
(Cu and Zs not 1ohm)

Buried
Unprotected 25mm2
Protected against corrosion 16mm2
Protected against corrosion and mechanical damage 2.5mm2

Not buried
Unprotected 4mm2
Protected against corrosion 4mm2
Protected against corrosion and mechanical damage 2.5mm2

The values have not changed from 16th to 17th.

Regards
Bruce