Five pages of debating trying to argue electricians are right and gasmen are wrong, and ignorant of what is really required, so to jump fence and see it from electrical regs side. ...
As has been said, there is no need for debate or argument since, as you have just quoted yourself, the electrical regulation concerned (411.3.1.2 of BS7671) very clearly states that extraneous-conductive-parts (only extraneous- conductive-parts) need main bonding ...
... so, if it's not an extraneous-c-p, it does not require bonding (and, as has been said, unnecessarily bonding something which is not an extraneous-c-p can increase danger).
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