The validity of the long-term visitor visa depends on the duration for which you apply and the corresponding fee paid upon submission of your form. The visa can be valid for 2, 5, or 10 years. The duration granted may vary on a case-by-case basis. If UKVI determines that you are not eligible for a 10-year visa, they may instead grant a visa for 5 years or 2 years. It is advisable to first apply for a 6-month visitor visa to establish a good record before applying for a 10-year visa.