Which signatories for a shotgun certificate are ok?
Many years ago when I lived in the UK, I had a science doctor sign my renewals and never had a problem. Your answer might be of benefit to others.
I think the legislation intends it to be your GP. However the list of potential signatories is very limited and in practice few people will know anyone on the list well enough to conform with the strict legal requirement.
Almost anyone will do as a signatory provided they have known you well for two years and are of good reputation.
Ideally this should be someone whose name appears on a professional register of some sort such as a teacher, lawyer, architect or whatever.
In my experience signatories are seldom rejected as being unsuitable.
A neighbour does mine and he has no particular qualification other than that we?ve known each other for decades and see each other several times a week.
I suspect he?d notice if I were going off the rails!