This is just made up, I'm afraid. It doesn't make sense to think that the phrase "the officer may demand" to see a certificate means that the holder has to produce one, and the officer doesn't have to ask for one. If the officer doesn't demand to see it, the holder is not still obliged to produce it.The cert holder has no discretion, the officer has.
“Shall” means no discretion for either party, “may“ introduces a discretionary element, in this case for the officer, but not the certificate holder.
Splitting hairs, but he isn't really required to. He does not commit an offence if he doesn't.The certificate holder is required to produce a certificate on demand.
Sorry if I worded it wrongly, I was thinking of the OP‘s question.


