2nd class blue Machin security from retail booklet, 2018, coded ROYAL MTIL M18L
The M17L version of these booklets, with security backing paper type 2, appeared in June 2018.
Cylinder numbers are W6 (blue) W1 (iridescent) W3 (phosphor).
SG U2963 - also used for other years
Price is for a single stamp.