A quick Google search of the street (Is it Prusom St, London?) shows the restrictions to be 0830-1730 Mon-Fri.
The alleged offence was at 1027, meaning that without a clock, on that single day, you could only have been parked for a max of 1 hour 57 minutes.
Whilst I don't think this would be a slam dunk on its own (my relative had a similar situation with no clock on a SYL, but there were underlying order issues), it might be a point to add to your formal reps too depending on what others think.