the 1940s (the latest stamp issues that I have seen one on to day is the 5½d Emu definitive).
Unless I have missed an article on these (please let me know if I have!!) there appears to be not that much
known about them except "you see them every now and again".
Here's an image of the two different types I am familiar with...
[attachment=0]tattersall opt.jpg[/attachment]
The underprint on the left (i.e. with sans-serif block capitals) is seen less often than the other.
I have started this topic to establish the following:
1. period of use
2. types of underprint
3. stamp issues on which they appear .... not that important but will assist with establishing 1. above
4. method of production
5. anything else other correspondents think should be recorded
If you have any information and/or images of TATTERSALL security underprints, please post here.