I would tend to use the descriptions from table 3.2 of Guidance Note 3 for identifying the type of installation. Which would not be domestic for a scout hut...
As IMHO Domestic accommodation general and/or rented houses and flats,
All refer to properties where people would be living, eating, sleeping, washing on a regular basis most days of the week. But are not open to normal use by the general public.
Whereas the table does list various buildings that are considered as open to the public.
Such as Church installations and Village halls/Community centres.
While some Scouts/Guides packs do use their own buildings, other use buildings/rooms attached or associated with churches and/or community centres..
I would probably categorise them as village halls or community centres..
If you have access to Guidance Note 3, have a look at pages 115/116 and see what you would think is the nearest description.