P.S....

The metal shed and metal framed greenhouse are both on a patio which in turn is sat on sharp sand followed by 100 mm mot1 hardcore.

The nearest bit of earth to hammer an earth rod into is the lawn and this rod would be at risk of lawnmower or strimmer damage.

Only alternative is to drill right through patio, sharp sand and hardcore and use an extra long earth rod...

I was going to use 20mm plastic conduit on all the cable runs between sub consumer unit and all the electrical accessories to improve both mechanical protection and implement "double insulation" between the conductors and the metal structures.

This is addition to using IP66 sockets and switches along with IP66 fluorescent lighting battens in both structures.

S.