Think very, very carefully before you report the passport to the UK embassy as lost. It may eventually become necessary but, once you do so, there will not any longer be any chance of a simple resolution of the problem. That will be true even if, not improbable, the passport materialises with your extension a day or two after you tell the embassy your passport is gone. Your passport will have been cancelled in the UK's system, and no longer be valid for trav
Correct, it's cancelled immediately on a computer system and I understand. not sure if true, but the British consulate told me, it would be flagged by Interpol.
If you get it back with a week, 2 weeks overstay it's fixable you might be able to do a border hop. or risk immigration, their rules seemed to be made up on the spot. But retirement visa applicant, money maybe, ok? Yes, I know it's a risk. You have to ask yourself, if you leave Thailand what are you leaving behind family? Do you have a place to go? and what gamble your want to take in country that only wants rich long term stayers? And is no longer the easiest or cheapest place to retire.
Good Luck and Ignore the Multimillionaire bar stool critics.