Who can be a referee for a customer applying from overseas
A referee for a customer who applies from overseas, must:
live in the UK or overseas (this does not need to be the same country as the customer)
pass our automatic identity checks (if they are a digital referee)
complete the 1 page form (if they are a paper referee (1 page form))
complete section 10 of the OS form (if they are a paper referee (countersignature))
They must hold (in order of preference), a current and valid (unexpired and uncancelled):
British passport recorded on our electronic passport records (this includes any variant type passport or British nationality)
Irish passport
European Union passport
United States passport
Commonwealth passport
If you know someone who is British you can get them to sign the form digitally. If you can't, follow the list of preferences from the guidance I shared above. Referee must not live in the UK.
All advice comes from personal research and experience and should not be regarded as professional opinion.