Richard Parsons has sent me a picture to share with you. Thanks Richard.
Although I have seen this reported elsewhere I do not think we covered it on this blog. From first glance this looks just like any other security stamp. It just goes to show that forgers are getting very clever.
The stamps are printed in litho, it appears to have security slits and overprint identifying that it comes from a booklet of six. Has anyone seen a booklet of six?
The letters MSIL can be seen clearly in the top right . I do not see a year code on Richards image.
From what I can gather it has no phosphor but varnished strips imitating the phosphor bars.