Ubonjoe, I must apologise for bothering you over this but an acquaintance of an acquaintance assures him that as he is married he need only show 400,000 baht to apply for his retirement extension and that this has always been the case..

He further attests that if you earn sufficient to meet income requirements and are a UK taxpayer, by merely printing off your annual tax statement from HMRC’s website, this document alone is sufficient for Thai Immigration.

If you have the time, your take on both of these would be very much appreciated. 

UJ will undoubtedly respond but as one that has been on both Thai Wife and Retirement extensions for over 10 years I can attest that those persons married to a Thai national requesting a Retirement extension must meet all Retirement extension criteria. That means 65K monthly income or 800K in he bank ( verified by bank letter.)

The caviate...the gotcha...is the interpretation of immigration rules by each immigration office and officers.  One might go to their respective IO and ask what is acceptable...to gain clarification. 

If married to a Thai he could apply for an extension of stay based upon marriage (not retirement).  He would need proof of 400k baht in a Thai bank for 2 months or a income of 40k baht.

To prove the the income he would need to show at least 40k baht of months transfers going into a Thai bank from abroad since the UK embassy no longer issue income letters.

Many thanks Asiaexpat, Puchaiyank and Ubonjoe.