https://www.gov.uk/countersigning-passport-applications
官網寫
If you’re applying outside the UK:
Your countersignatory must have a current British, Irish or other EU, US or Commonwealth passport.
If they have a
US, Commonwealth, or non-British or non-Irish EU passport, you must include with your application
a colour photocopy of the page with their photograph on it.
有冇人試過寫信話提供唔到副簽人嘅護照個人資料頁,而又成功續到期?
(知道後果自負但想知有冇成功例子)