Many small businesses are started by people working in their own homes.
Home-working does not necessarily require planning permission. Permission is not normally required where the use of part of a property for business purposes does not change its overall character.
For example: the use of one room as an office, or a small child-minding business, would be unlikely to change the character of the house. Therefore, this would not normally require planning permission.
Once the business or non-residential use of the property has intensified, this counts as a change of use, for which planning permission is likely to be required.
This is especially the case if the business or non-residential use generates visitors, traffic, noise or fumes over and above what might be expected of a household property.
If you are in doubt you may apply for a Lawful Development Certificate (LDC) for the proposed activity, to confirm it is not a change of use and still a lawful use.