My usual supplier was out of a few urgently needed items yesterday, so I had to go to the nearby B&Q (big DIY store, very similar to HD even down to the orange color scheme).
Here's the entire printed wording on my individually wrapped earth clamp:
Earth Clamp EC 15/2 - 19749BQ 195mm to fit 35-50mm approx. For indoor or outdoor use. Not suitable for use on pipes with non-conductive surfaces. Accepts earth cables A-E 2.5-16mm2 Not for use on the sheath or armour of a cable.
Ah well -- So much for bonding to the PVC water pipe!