Many small businesses and other non residential uses 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 dwelling-house for business purposes does not change the overall character of the property's use as a single dwelling.
For example, the use by a householder of a room as an office, or child minding business complying with the Department of Health's standard recommended ratios, would be unlikely to mean that the character of the house's use as a single dwelling had ceased and would not normally require planning permission.
Once the business or non-residential use of the property ceases to be ancillary to its use as a single dwelling because, for example, the business has grown and the use of the dwelling for business use has intensified, a material change of use for which planning permission is required is likely to have taken place.
The likelihood of a material change of use taking place may be indicated where the business or non residential use generates visitors, traffic, noise or fumes over and above what might be expected if the property were in use as a single dwelling without any ancillary use.
If you are in doubt you may apply for a Certificate of Lawful Use for the proposed activity, to confirm it is not a change of use and still the lawful use.