5 May 2011 - William Morris prestige stamp book - 50p.
The definitive pane is self-adhesive, with 5p, 10p & 50p stamps. Only the 50p has the iridescent security overprint, MPIL M11L.
These are printed by Walsall (or Cartor - information from Royal Mail was inconclusive and contradictory).
Catalogue number SG U2917 was also used for other years' stamps.