O.K, I`ll chuck my two pennorth in....
Accepted that "hard metal pipework" doesn`t include lead; I`d still clamp it. Reasons being:
1. Lead. Good conductor( see old REC sheath.)
2. If you`ve looked at an old piece of lead pipe, the wall thickness is pretty intense. You`re more likely to puncture copper than lead with a clamp (cur for anyone who`s managed this feat to shoot me down!!)
3. I`ve bonded the incomer for 20 years+ I`ve recently seen sparx (see Dom. Inst. ), who`ve bonded polypipe / alkathene pipe, and despaired over the future of our industry. I have even been advised (by an NIC area engineer), to have the plumber provide a 500mm stretch of copper in his poly install within a bathroom; so I can bond to it. U leave the outcome of that cinversation to the imagination, as admin would frown on a verbatim quote.
Bond (age) is good. So the missus informs me, anyway.
p.s. Thanks guys, Egypt was Awesome