You are likely to be self-employed if you meet the following tests:
You agree to do the work, but you can send someone else to do the job for you, for instance, a builder who can send another person with similar skills in their place.
You probably have several customers at the same time. You can do the work how, where and when you like, for example, a writer who agrees to write a book and can write whenever they want to, as long as they meet the deadline set by the contract.
You run a business and take responsibility for its success or failure, such as a joiner who has to redo unsatisfactory work, and cannot charge the customer for the time spent redoing the work.
You provide the main items of equipment or specialist tools you need to do your work, such as a pick-up truck, or scaffolding.
None of these tests are conclusive.
Where can you find more information?
For more information about who is an employee and who is self-employed for tax and NIC purposes: