5 May 2011 - William Morris prestige stamp book.
The definitive pane is self-adhesive, with 5p, 10p & 50p stamps. Only the 50p has the iridescent security overprint. These are printed by Walsall (or Cartor - information from Royal Mail was inconclusive and contradictory).
The 5p red-brown (Royal Mail colour = ash pink) Machin security stamp was issued in counter sheets on 8 March 2011 printed by De La Rue.
Catalogue number SG U2993 is used for both printings, but the book printing is quite different to the sheet printing.