My son has a casual (zero hours) job in a sports centre near our home, and is applying for a similar job in a sports centre near his university term-time address. He needs a reference, but his current line manager hasn't responded to his request (he's generally bad at responding to emails). If he asks the HR department instead, are they likely to give one? It'll be fine to just confirm he works there, as he already has a character reference from someone else.