2nd class blue Machin security from retail booklet, 2016, coded ROYAL MTIL M16L
The M16L version of these booklets, with security backing paper, appeared in mid-April 2016.
Cylinder numbers are W6 (blue) W1 (iridescent) W3 (phosphor).
In December 2016 further printings of the booklet were made on covers with new type of security printing on the backing paper, this we refer to as SBP2. SG U2963 - also used for other years
Price is for a single stamp.