Question about Referee and Identity apply mn1 outside uk?

[Microlam]

Hi there,
I have to apply the MN1 form for my new born baby. He is in Japan now
On the section 5 referee and identity. I need to find 2 Referee to sign this form. One referee should be a professtional, who has engaged with the child in professional capacity.

I plan to ask my son's doctor who is the person delivered the birth for him.
But he is Japanese. He could only can sign the form and provide the cover letter to confirm the photo identity of my son. But the uk citizenship passport no section.Can I leave it blank. Because he is not british and he don't want to write his passport no.
In this case, Is it ok for submit it the form or too Risk because he don' put his passport number?

Looking for anyone to advise

[neoseal]

Professional referees don't have to be British, hence no passport number required.

[Microlam]

Thx for your advise