When our son returned from the USA last September he had his UK passport but no job and no NINO when he opened his bank account which was very important because he needed to transfer his money from his bank in the USA. Fortunately he was living with us and the bank accepted a letter from us plus a utility bill made out to us. We had been customers of the bank for over over 30 years but even a statement from them to our address was not good enough, it had to be a utility bill, apparently a government regulation rather than a bank rule. His NINO was not needed, just a promise to notify the bank once he had received it (some weeks later).
I don’t know how folks without this sort of support manage to open a bank account.