What steps should I take to transfer my visa to a new UK passport upon returning to Thailand?

When returning to Thailand with a renewed UK passport, it's essential to present both the new and old passports upon arrival. After arriving, you should visit the immigration office to transfer your visa to the new passport. Take note that the specific requirements may vary by immigration office; for example, if you hold a retirement visa and are at the Bangkok immigration office, they may request financial documents such as a bank book and statement. Some expats have encountered requests for additional documentation, such as a letter from the embassy, although these can sometimes be disputed based on individual experiences.