Update.

They cancelled my penalty as it was a "first offence". The reason I got the ticket they said was for "The vehicle was parked in a designated Disabled persons’ parking area without a
valid Disabled Blue Badge / disc/time clock displayed in accordance with the
conditions of use of the Disabled parking scheme.
The disc/time clock displayed for inspection in the vehicle alongside the Disabled
Blue Badge was set to show the time of arrival of the vehicle at the location of the
contravention as approximately 7:00 (see the enclosed photo images). The
vehicle had therefore been parked in excess of the maximum permitted stay of 3
hours clearly indicated by signage". The clock was not mentioned on the penalty notice. Still I’m happy. It’s worth appealing, there is nothing to lose.