According to the Islington Gazette, Islington council could be facing mass appeals and refunds on PCNs they have been issuing since 2008. It seems to stem from a PATAS case (#2130131169), in which it is noted that not only did the signage in the location not meet requirements, but also the wording of the PCN itself was suspect.
It has something to do with how appeals can be made before a Notice to Owner is issued, and what happens afterwards. Apparently the wording in question has been on Islington PCNs since 2008, potentially opening all of them for appeal. The value of those PCNs approaches £77.5 million.
Islington have only recently had to agree to cancel and refund nearly 11,000 PCNs worth £1.4 million issued in the last 6 months for a penalty location that didn’t comply with local traffic regulations.