Great Britain (Scott 261, Sg 488) Overprint Help

Looking for help on how to describe the overprint, and an issue on the back. This 2d King George VI stamp is the lighter orange, hence Scott 261, SG 488. The overprint says, "Received For / John Barker & Co. Ld." On the back it appears that the stamp was laying on another document since the lettering is reversed. I can see, "Received / with thanks / the sum ..."

Is the overprint some type of advertisement put on the stamp before it was used, or is this some private overprint? Thanks in advance. (Also, please advise if soaking would remove the interesting lettering and horizontal lines on the reverse.)
Front

Back

Back reverse image

Revenue use. The company that collected the tax had the stamp overprinted with its name to prevent abuse or theft.

http://www.gbos.org.uk//index.php/O...t_Revenues/2

The paper from the document to which the revenue stamp was attached is still attached to the back. If you soak the stamp, this should come off and you will be left with the normal, overprinted stamp.

As GB stamps were used for both postage and revenue purposes, companies requiring stamps for the latter use (on documents) would often overprint them - similar in effect to a perfin.

Thank you for the very quick replies. I'm not going to soak, preserving the interesting back, and will file it with the link and great information.

There are earlier threads along these lines. Here's one of them:

https://goscf.com/t/73010