Help On Filing Deputy Papers In C.O.P

[INVICTAGUY70]

My father has been assessed as mentally incapable of managing his affairs and I'm in the process of filling for deputyship via the COP.
I can't find his NI number anywhere and it's obviously needed. The institutions that have it can't give it to me and therefore it's catch 22.
Anyone been through anything like this? TIA.

Have you a really good rummage in his house? NHS cars? An old tax coding notice? Post Office savings account? Anything from DWP / benefits?

I've gone through the whole process once already for my father, and am just about to do the same for my mother, I feel for you. So many forms!

Card not cars!