Would a Public Servant qualify as a ''Professional''? I see Civil Servant is on the list but not Public so I assume no? Also on the application it asks me of my relationsip to my referee's, if I put friend would that be alright or do I have to a more business sort of relationship with them?
My suggestion is to think through the process and ask yourself: "What problem is the Home Office trying to resolve or answer?"
Basically, the Home Office wants to know two things:
-- You are who you say you are,
and
-- possibly more importantly, that the referees are who you say they are, and that they can thus vouch for you when you say who you are.
How would the HO confirm information about your referees?
During my application process, I saw that the vast majority of the entries on the referee list are ones where there is some sort of registration or organisation available for the Home Office to verify that person..
If you list as your professional referee Mark Jones, accountant, the Home Office would have an organisation to contact and ask: "Is Mark Jones a registered accountant? And if so, when was he first registered? And how can we contact him?" (Does that contact info match what you said?). And not just your neighbor who comes over every so often and helps you balance your bank account statement, whose name is actually Jack Jones and who may have only lived in the country for a couple of years (he may say 5yrs) so can't have known you long enough. Please note that I'm not saying that Mark Jones is necessarily a ne'er-do-well or a member of a foreign gang. My point is how can the Home Office confirm what your application says about him should they want to so confirm?
So, I highly recommend that you try to use a profession on the list. If not able to do so for whatever reason, try very hard for your referee to have some sort of professional accreditation from a recognised organisation which the Home Office can contact.
Otherwise, you're dependent on the thoughts (and mood) of the HO individual reviewing your application. You want to avoid that dependency.
Also in my view, if my neighbour happens to be an accountant, I would see no problem in using her as my professional referee even if she did not do my taxes.
Similarly, I would strongly advise to use as a personal referee someone who is residing in the UK. (Even if it'might not be a strict requirement. I don't know the requirement.)
Again, think through the process.
Would a person in Singapore be able to vouch that you have met the requirements? Such as having resided here for the requisite period of time? (Your mailing address alone wouldn't necessarily prove physical residency. Why chance it if not totally necessary?)
I was lucky in several ways: my accountant had done our taxes for the previous 8 years and was a perfect professional referee. And I have had the same landlord since 2012 and he was overjoyed to be my personal reference, helping me to obtain citizenship in his beloved country. (Be a good tenant, and be totally lucky like I was and end up with a good landlord. I also pointed out to him that when I obtained UKC, he would no longer need to check on the government website to ensure that I had a right to rent here.)
Best of luck to you.