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This answer Requirements for obtaining a long-term UK visitor visa (2, 5, or 10 years) indicates that you may need more than a performance history of 3 short term visit visas. The only way to find out is to apply, weighing up the potential benefits if youβre successful vs the extra cost if not - perhaps applying for a 2 year visa first would improve your chances (you could probably squeeze in several visits over the period to make it cost-effective, if you timed your application carefully)