Found this on Government web site, so I would say no he can't.
Who can sign forms and photos
Personal relationship
The countersignatory must:
have known the person applying for at least 2 years
be able to identify the person applying - eg they’re a friend, neighbour or colleague (not just someone who knows them professionally)
They can’t be closely related or involved with the person applying, eg:
related by birth or marriage
be in a relationship or live at the same address as the person applying
https://www.gov.uk/countersigning-passport-applications