I am grateful for your detailed response. Obviously. I am looking for the simplest route to providing 'evidence of funds'.
This is item 4 from the MOFA website:-
"Financial evidence: amount of no less than 500,000 THB, e.g. bank statements, sponsorship letter".
IMO, if a PSB summary is acceptable to, say, UKVI then there is no reason why it should not be acceptable to MOFA...................I fully accept that acceptance, or otherwise, will be at the behest of the approver.
You may wish to review your comment about no statements being available.
How to get NS&I-branded statements online
Firstly, you need to register for our adviser online service. This will give you easier and faster access to information on your clients’ NS&I holdings, so is worth doing anyway, but it’ll also give you access to NS&I-branded statements.
https://www.nsandi-adviser.com/helping-us-help-you-nsi-branded-statement-requests