I just successfully used the emergency extension letter from the British embassy at Korat immigration.
I printed the letter and the email from the FCO as advised here and they were happy with that. So thanks for the advice.
Got the under consideration stamp and have to go back in two weeks.
They did say that if the situation carries on for an extended amount of time I can just get another letter from the embassy and use it again.
TLDR : Answer Summary
A user successfully utilized an emergency extension letter from the British embassy at Korat immigration, providing useful insights on the process. They printed the letter and an email from the FCO, which were accepted without issue. The user received an 'under consideration' stamp and noted that they can obtain further letters if needed due to ongoing circumstances.