As a British citizen, you are not the subject of the Crown in the sense of being personally owned or controlled by the monarchy. The Crown is a constitutional entity that represents the institution of the monarchy and the constitutional arrangements that govern the functioning of the state.
In the United Kingdom, the Crown and its powers are defined and limited by the constitution, which includes various constitutional documents, laws, conventions, and traditions that have evolved over time. The monarchy acts in accordance with these constitutional principles, and the powers of the Crown are exercised by the government, which is responsible to the democratically elected parliament.