Looks to me more like an exposed conductive part.

Other than it's stuck in the ground, so provides some path to true Earth for diverted neutral currents...

That said, it's likely to have a ground resistance of several tens of Ohms, so the current flow is likely to be very restricted - so not a huge worry for a single column (but maybe you wouldn't want to rely on the 0.75mm² c.p.c. in a flex to the lighting head).

Maybe less restricted if you had many columns (long drive to a country mansion) - where the overall resistance of many in parallel could be reduced a fair bit.

Steel column have been debatable in terms of exposed- or extraneous- for a long time. Are they part of the electrical installation, or just supporting/enclosing it? If you had unsheathed singles inside it should be an exposed-conductive-part and therefore cannot be an extraneous-conductive-part (perhaps counter-intuitively, but that's what the definitions say). If sheathed cables inside, but the column in contact with a class 1 lighting head, then extraneous-conductive-part would seem to fit.

   - Andy.

Quite - it is not always clear what the risk is for which we need the CPC .. to carry a diverted neutral current needs a big one, comparing to the DNOC cable, while to blow a fuse doesn't need anything larger than the final circuit  supply rating,  and to trip an RCD probably does not need a CPC at all if the thing is planted in the ground.

The regs do not really make the distinction.

mike

Quite - it is not always clear what the risk is for which we need the CPC .. to carry a diverted neutral current needs a big one, comparing to the DNOC cable, while to blow a fuse doesn't need anything larger than the final circuit  supply rating,  and to trip an RCD probably does not need a CPC at all if the thing is planted in the ground.

The regs do not really make the distinction.

mike