Yes, extending a UK Standard Visitor Visa is only possible under limited circumstances, not for general tourism. You need a powerful reason to stay longer. Some of the acceptable reasons to extend your visitor visa are:
- If you receive private medical treatment and can prove that you have paid for previous and ongoing bills.
- If you are an academic, visiting for a specific research project that requires additional time.
- If you need extra time to retake a Professional and Linguistic Assessment Board test.
- If you face a family crisis or an emergency.