From 17 February 2009 1st and 2nd class Machin Definitives and higher-priced 'make-up' values at 50p and £1 were produced as self-adhesive stamps with enhanced security features including semi-circular slits and an iridescent 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 the Business Sheet 1st class, with the ROYAL MAIL overprint changed to ROYAL MBIL - SG U2948 (both types)
Available in two types:
Type a - These were first issued with two U-shaped slits at the foot on each side.
Type b - The later version has a gap in the Us at the top (or bottom) of the curve.