Earth testing of large wind turbines in UK and internationally

[electrickiwi]

Is anyone familiar with the requirements for (or have experience with) earthing system testing of large wind turbines or other tower structures (particularly in the UK but I'm interested in other international input too)?
Specifically, what sort of testing is required to verify the earthing connections down the length of the structure prior to putting it into service? Will an earth fault loop impedance test at the tower top be sufficient or is a high current micro-ohmmeter test necessary? If the latter, is a tower-length set of test leads required or can the measurement be done wholly up-tower by using the neutral cable that runs up separately but is bonded to earth at the base?

I realise the steel tower generally provides the majority of the down-conductor path, but there are still joins between tower sections, and slip rings or flex cables for bypassing bearings, plus cable lug connections up-tower, any of which could be a poorly made joint.

Turbine blades with internal lightning conductors must need the more specialised equipment (right?) since the conductor is generally only exposed at blade tip and root...