Scotland, Bank of Scotland 1.6.2016 P-131x PMG Gem UNC 66 EPQ 10 Pounds (Experimental XX Prefix)
While at first glance this may appear as a regular polymer 10 Pound, the XX prefix in the serial number indicates that this is a rare pre-production experimental issue, that was never meant to be issued for circulation. They were distributed to vendors to test new machines and were supposed to be returned, but a few pieces escaped this fate and entered the collector's market. The exact number of pieces is known, but judging by the infrequency of offerings, it must be very small.
PMG Population in 66 EPQ: 4 (3 Finer)