Perhaps criteria would be better but I don’t think it alters the fact that (again specifically to Scotland) when you are within the thresholds set you do not require planning permission. Go beyond the thresholds and you do require permission. It’s that simple for guest houses or B&Bs here. Scottish Use Class Order:
Class 9. Houses
Use–
(a)as a house, other than a flat, whether or not as a sole or main residence, by–
(i)a single person or by people living together as a family, or
(ii)not more than 5 residents living together including a household where care is provided for residents;
(b)as a bed and breakfast establishment or guesthouse, where at any one time not more than 2 bedrooms are, or in the case of premises having less than 4 bedrooms 1 bedroom is, used for that purpose.