In the UK, a Master's thesis is typically considered a form of scholarly research that is not considered as a published work. Instead, it is presented as part of the requirement for obtaining a Master's degree, and is usually only available in a limited distribution within the academic institution or department where it was completed.
However, some universities in the UK do allow students to deposit their Master's theses in a university repository or an online repository, which can make them accessible to a wider audience. In such cases, the thesis may be considered as a form of "grey literature", meaning it is not formally published but still accessible to the public.
It is important to note that the specific policies regarding Master's theses can vary between universities, so it is always best to check with your institution for their guidelines.