20 March 2018 - 1st class deep scarlet Machin definitive M18L MCIL
The first stamp to be re-issued with a 2018 year code this appears in the retail booklet for the Centenary of the Royal Air Force.
The Royal Air Force, Red Arrows, and Dad's Army booklets have definitive stamps with blue phosphor.
The Hampton Court, World War I and Harry Potter booklets have definitive stamps with blue phosphor, and with the transparent iridescent ink fluorescing yellow - see 2936a.8a
SG number U3027