@Heidi *******
as British citizens, you cannot use the 12-months income financial statement for the 1-year extension in Thailand. You need a minimum of 800,000 THB in your Thai bank account in the first year. And that's EACH of you. If one of you wants to apply for the "trailing spouse Non-Imm-O visa" which has no financial requirements, then the London embassy probably will require the husband to be on a 1-year Non-Imm-O/A visa. You will have to ask them via email