How can my husband transfer his Non O Thai visa to his new UK passport?

To transfer a Non O (marriage) Thai visa from an old UK passport to a new one, your husband typically does not need to take any action. He will receive the old passport back with a corner cut off and should keep both passports together. If he has a yearly extension of stay, he can take both passports to the immigration office to have the existing stamps transferred. If he holds a year-long, multi-entry Non-O visa, he should carry both passports when entering or exiting Thailand until the visa in the old passport expires.