Proof Of ID?

I just got a job at Mcdonalds, and my welcome meeting is in less than a week. The emails aid to bring my asylum and immigration documents (birth certificate and NI number letter) AND my ID. As i don't have a passport i don't know what classes for ID.

I'm 16 so don't have a driving license or anything like that. Does my NI letter combined with my birth certificate count as ID? Someone told me once that my mum's passports proves my ID as i am listed as her daughter in the emergency contacts, but this is just written in so t doesn't seem right.

What else can be used as ID which is not a passport? Please help! Thanks.