The above details on taxation are interesting, but seem to relate to setting up a limited company. However, my self employment, because it is small turnover, is not as a limited compay, or a registered company at all, merely as a self employed sole trader. I claim tax relief through my tax return annually for any training and renewal costs, by putting them against my profit (or loss). I work mainly for one client. I have an income as a emploee also, which is PAYE taxed. It is this tax which I claw back if I have overpaid on the year due to my sole trader self employment making a loss if, say, a big training bill came in that year.
I have no protection in the case of my company going bust, like a limited company would give: they can come and get my house. However, as I have sole control over incomings and expenditure at a very small and manageable level, with little fixed cost, this is not really a risk. The cost of setting up a limited company with directors and a named secretary far outweighed any benefit to me. My tax situation seems simpler than the IR35 status you describe.