2nd class blue Machin security from retail booklet, 2017, coded ROYAL MTIL M17L
The M16L version of these booklets, with security backing paper type 2, appeared in mid-June 2017.
Cylinder numbers are W6 (blue) W1 (iridescent) W3 (phosphor).
SG U2963 - also used for other years
Price is for a single stamp.