Discovered April 2012 - no specific date of issue, but first discovered then on eBay.
Security Definitive stamps with U-shaped cuts and iridescent text.
12 x 1st class gold booklet - first issue with year code M12L and source code MTIL. This gold booklet was printed in late 2011 and made its surprise appearance in April, ie after the Diamond Jubilee 12 x 1st booklet was issued on 6 February 2012. Never available from Royal Mail's philatelic bureau.
Printed by Walsall Security Printers.
Printers imprint on reverse now removed
Forest Stewardship Council certification logo on the reverse (not the first time as this also appeared on late 2011 booklets on 25.10.11 but we no longer have those in stock).
SG catalogue number MF5c - also used for late 2011 issue.