S
Silly Sausage
The 23k "rule" is wiring regulations, not PME regulations. Bonding, which is reqd in this situation and creating an equipotential zone ensures the safety of the area. What does create danger is bonding bits of pipe etc and not others, as enviged by the wiring regulations. For example, bonding an oil pipe but not a water pipe "because its got an insulated insert" Regards UKPN, and mind how you go.
If our man tests these metal sinks in question on a hot day with nobody working and nice dry floors, no way will they need bonding.
I'd defer the problem to the summer.