Does anyone have experience with this 'administrative procedure' called declaration of income from the French embassy?   It is a self declaration and they provide a form letter stating income declared.  I have seen an example of this letter and understand that it is acceptable to the Thai immigration authorities.  I am a taxpayer and homeowner in France although I hold a UK passport.  

and citizenship.  I live in Isaan, near Buriram and imagine that I will have to go to BKK to do this in person there.  It seems straightforward enough but who knows?  Any comments or advice gratefully received.including ideas about a venue to get this done not in BKK.  Thanks Very much.

Not aware of what their procedure is. Perhaps you can find the info here: http://www.ambafrance-th.org/-Actualites-Consulaires-790-

I am not sure they will do it for you since you are not a French citizen I suggest you contact them about doing it.

Also I am not sure immigration will accept one from the French embassy since you will be using a UK passport for the application.

You can use your income from France to get a income letter from the UK embassy and it is done by mail.

Info is here. https://www.gov.uk/government/publications/how-to-obtain-a-pensionincome-letter-for-thai-immigration

Thanks Mr ubonjoe.  It looks the business and I wrote to them.  Will post my experience when it occurs.