What should I do if my UK visa lacks sufficient validity for my Thai visa application?

Apply from your home country its always easier

You usually can't travel internationally with less than 6 months validity left on your passport, so I'm not sure that you're going to be able to go to another country to apply until you get a new passport.

You haven't stated your nationality. some embassies initiate extra scrutiny from some nationals of foreign nations. These extra requirements are usually noted on the embassy website.

Did you get your application rejected yet or have they just asked you to renew your visa (and you can’t)?

Firstly can you call or visit the embassy to talk about the situation?

As you say, explain that it does not mention visa validity anywhere and you’ve made a lot of effort to apply in London and it’s your current location and home for 2yrs, you meet all the DTV criteria etc and you’ll be leaving for Thailand straight away.

It might be possible to get approval on this application, if you speak to them and explain the situation.

For example, how much longer do they want on your visa? Would getting a tourist visa after this one expires give you enough time?

The London embassy seems to have been very quick and efficient with processing. I would speak to them and appeal for them to reconsider.

I would not suggest applying from a country you’re not in. They ask for proof like passport stamp and it’s against the DTV conditions and you could get blacklisted if caught.

Good luck with it

What is your passport nation?

The requirement is that you are supposed to be in the country though which you apply. You will need to show evidence that you are there. Many require residency as well. Your best option is to fly to a neighboring country in Southeast Asia and apply. Unfortunately your fee for the UK-based application won’t transfer.

First of all: no refunds, no matter what.

As per the visa, it seems they want to be sure you're "a resident" in the UK. But I understand that in most cases we can't just extend visas whenever we want. In Korea, for example, long term residents can extend their current visas only when less than 4 months remain on it.

Totally possible but runs the risk of rejection if found out