Leave to Remain

Hi, my father is a Canadian living in the UK and has done so for years, however he has no passport, I am effectivley looking to get this for him but am confused as of what to do. I was wondering if anyone could give me some information as of what steps to take, which forms are needed and how to obtain them.
I would be extremley greatful to anyone who is able to help!

Passport for where, Canada or UK? Is he Canadian citizen, or UK citizen?