In Scotland there are two types of small farm.
Crofts are legal entities and are mostly in the Highlands and Islands.
Smallholdings can be anywhere in the country and do not have legal status or attachments.
If you are looking at a specific piece of land that has been referred to as 'decrofted' then you need to find out about the legal issues regarding croft land.
All planning applications are made to the relevant County Council, and usually by an architect who has drawn up either specific house plans, or an application may be made for 'planning in principle' which just gives general consent, and specific consent will have to be applied for at a later date. To my knowledge that applies whether it is a croft, a smallholding, a farm, or a piece of land
Hope that helps?