For what it's worth, I called the Passport Advice Line stating that I was applying for naturalisation, and wanted some clarification in terms of what a "Professional Person" is. The person I spoke to said that if you need a degree to do the job, then your referee would be considered "professional." If in doubt, but looking for some confirmation from a source other than UKY, the number for the Passport Adviceline is: 0300 222 0000
I had rung up, because "Pharmacist" was on the list, and I know several registered (but not practicing) pharmacists through work, so I wasn't sure if the fact that they weren't practicing mattered or not. Turns out it doesn't!