It would appear from the Embassy's latest "Dear Pensioner" letter (downloadable from https://www.gov.uk/government/publications/how-to-obtain-a-pensionincome-letter-for-thai-immigration) that it is now only possible to apply for these letters in writing and no longer through personal trips to the Embassy. Clearly this will be a pain for Bangkokians in particular - as well as for Chiang Maians if this also means that they are no longer able to apply in person at their local Consulate.

The letter merely says "there is no need to apply in person" , it does not exclude personal application being made.