Passport Application - Countersignature

Hi,
I have a question concerning the online application process. More specifically, the stage requiring the countersignature. How is this done? What does the countersignatory have to do? Can someone explain all of the details? Thanks for your time.

Regards,
Anders

You state a referees name and email.
An email is sent out to the referee by HMPO.
The referee is required to confirm the picture and fill in a few details such as their own passport and I think relationship to you.

That's perfect! Thanks.