My understanding is that, unlike incorporated / limited companies, unincorporated associations such as sole traders and partners are subject to income tax rather than corporation tax, as well as National Insurance contributions (NICs) of course, since they’re not legally separate from their businesses.
Am I right in thinking that income tax is levied on the net profits of the business, less any allowable expenses for line items such as electricity costs for your business premises, and that for partners, since they share in the profits as well as the losses of the business, they will be subject to income tax that will be levied upon their share of the profits?
Broadly speaking yes. For a partnership, there is a “partnership return” that declares the income, expenses, allowances and overall profit or loss for the partnership as a whole, and the apportionment of that profit or loss among the partners. Each partner’s share of the partnership profit figure then counts towards their personal income on their own SA tax return, added to all their other sources of income, and their tax and NI calculated on the final total.
For a sole trader there’s no separate return for the business as distinct from the individual, it’s just a section of your SA return (self-employment, either the “short” or “full” version depending mainly on whether your turnover meets the VAT threshold).