In the UK workers are taxed differently based on whether the work arrangement looks more like self-employment or employment.
Here's an example by HRMC for self-employment:
Alan is taken on by a manufacturing firm to design and build a new website. Alan and the firm have agreed a price for the job and when he will deliver the new website. Alan will mainly work at home, using his own equipment to complete the task. Alan is free to work for other clients but faces a contractual penalty if he doesn’t deliver the website on time, to the agreed standard. This represents a significant financial risk to Alan if he fails to deliver the final product as agreed.
And this for employment:
The manufacturing firm needs someone to maintain and update the new website. It hires Jemima to work for three days a week, eight hours each day. The firm provides Jemima with a laptop so she can work at its offices or at home with permission. She reports to the head of the IT department and must follow their style guide and format to update the website. The firm is responsible for providing and updating the software Jemima needs to do her work. If Jemima has to work longer than her contracted hours, she will be paid overtime. Jemima can work elsewhere on the days she is not working at the firm, with their agreement.
What is the argument for treating the two differently for tax purposes?