The Home Office requires passport and naturalisation applicants to have a 3+ year personal acquaintance of professional standing to act as a referee. This provision is antiquated, futile, discriminatory, absurd and a nuisance to both referee and referred. It's time to keep up with the times.
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The list of persons deemed of professional standing is published in:
https://www.gov.uk/countersigning-passport-applications/accepted-occupations-for-countersignatories