Question to the HM Treasury:

To ask the Chancellor of the Exchequer, for what reason HMRC do not accept Commonwealth, EU or other overseas passports as proof of identification for people completing their self-assessment tax returns online.

This question was answered on 4th February 2021
HMRC do not have access to other countries’ passport databases so they are unable to check the validity of overseas passports in the same way as they can with UK passports.