You get the certificate of life from the UK consulate and it is free (if for the UK government). But note that the consulate is having an extended closed period over the new year due to holidays.

The Consulate has stopped doing Proof of Life now. I tried.

I was in the consulate last month and they had a notice up saying they were giving certificates and they were free if for a UK government office. I can not find anything specifically saying this on the embassy website but their fees table says:

"Signing a declaration of existence (except if required by a department of British Government in the UK) £15"

Which I take to mean no fee if for British Government.

I've attached the fees table (I hope).

(no, it didn't attaches, maybe the link will work https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/352521/FeesTable_Customer_10_Sep.pdf)

I sent the forms for my wife and I, by normal Thai Post on 12th December.

I phoned today to check if they had been received. They have a special Life Certificate section (you press "1").

The guy was most helpful. He confirmed that they had received them, and after asking us a couple of security questions he said he had inspected the forms and they had been accepted.

I used Skype, very good sound quality, 12 minutes call cost 21p or 10 baht.

One less thing to worry about, until the next time.