From 17 February 2009 1st and 2nd class Machin Definitives and higher-priced 'make-up' values at 50p and £1 will be produced as self-adhesive Stamps with enhanced security features including semi-circular slits and an irridescent overprint.
These initiatives are part of the on-going development of security features for Stamps. The slits are designed to inhibit the removal of these Stamps for fraudulent sale and re-use. The overprint features the words 'Royal Mail' in a pattern reminiscent of security features on banknotes.
This is a cylinder block of 6 of the 2nd class Large letter stamp from ordinary Counter Sheets, from the 2011 issue, coded MA11, discovered in early 2011.
SG Catalogue/Norvic cross-reference table - click here. See other blog entries for the history of the development of security Machins.