You have quoted the wrong Regulations.
No I have not.
And here's another one - 542.1.3.2 Precautions shall be taken against the risk of damage to other metallic parts through electrolysis
There is a Regulation specifically and overtly requiring sleeving to be fitted.
I have quoted three of them, what number is the other one? There used to be a reg about s/o earths to back boxes being sleeved, but I think it's been removed.