Self-Assessment (personal tax account) for minor

My minor nephew has to complete a self-assessment. Naturally, he receives assistance from his parents and myself in this regard. Last year, an online personal tax account was set-up in this regard, which worked well, and he was able to file online. This year, the online account required 'age verification' on login, with the further message that he was unable to complete the verification process due to being too young (under 16, from memory). So, a paper form had to be obtained. Can a minor have an online personal tax account for self-assessment? Thanks.

Hi,
There is no reason why a minor cannot have a personal tax account. You will need to contact our online support team for advice on log on issues. 
Technical support with HMRC online services
Thank you.

I recently had an email to say that a new response had been posted in this thread. I get here to find no new response...ho hum.. Anyway, an update. I called up both HMRC technical support (a labyrinthine process in itself), and the standard HMRC helpline. The upshot apparently is that there has been an 'IT upgrade', so that now you can only do self assessment online if you have an NI number (why isn't a UTR good enough?). Can a minor get a NI number assigned? Of course not, not usually, Kafkaesque is the word that springs to mind. The hard copy letter of complaint has gone in.