If you can't raise the b400k needed for a marriage visa even with a loan, your options are limited to 60 day visa exempt on arrival with a 30 day extension, then leave. You might be able to do that twice, but doubt it can be done a third time.
IO will be more interested that b800k was not held in the account for 2 months post application, and/or b400k was not in the account for months 3 to 9 before going back up to b800k. As the financial requirements are not met, the visa is no longer valid.
No legislation is perfect. Any legislation that requires the decision of an individual based on evidence, or the balance of probability is subject to that individual's conscious or unconscious biases. If the requirement are satisfied there is no problem. If not there may be routes to appeal ( Not for UK immigration decision made outside UK, as an example) If people try to subvert or interpret the rules to suit themselves, particularly in a foreign language and culture it will never go well.
Steve Rew 😀 If you ever told a UK official to 'do their job' you would be buried in the paperwork for months! Afaiu, the actual Thai legislation requires a statement from the national's government that the monthly amount paid in is a pension. The UK govt. (along with a few others) will not supply the required pension certification so that route is effectively not available to UK nationals. Having to trawl through excessive paperwork in a foreign language is certainly something I can understand the IO not wanting to do. The only thing they are interested in is do you qualify or not. On my last renewal I gave them statements/certifcates for all my Thai bank accounts, each of which had more than the required amount in and they genuinely got confused and after a few moments explained they only need 1 account that qualifies the rest is just extra unnecessary checking, copying and stamping. Then asked me to choose 1 account to use and gave all the others back. The b800k is only ~£25k dropping to b400k for the mid term 6 months, providing you are accurate with the amounts and dates is easy and simple. The 'loss of interest' on Thai held funds is negligible when you consider how the GBP/Baht exchange rate is doing, and less than the 14k requested by the agent (who you are likely to be tied to for future renewals as something will have been 'overlooked' on the inital application. TiT.