Appeal sent will go the POPLA route as suggested.
If this letter is the 100% the first one you have received it should be cancelled no problem.
I got a ticket last year for stopping at Southampton Ferry Port to pick somebody up and the ferry was late. I went onto MSE, and actually found the land isn't enforceable because it comes under port authority. I appealed it, the company declined the appeal thinking i'd suck it up and pay. Went to POPLA, sent my evidence in.
The never contested it at all, 2 days later was told it was cancelled. They just hope people will suck it up and pay, it costs them a lot to keep chasing these things.
But like people have said you should not ignore them anymore. But never identify the driver, because thats who the contract is with.
If you search for the specific carpark on MSE, you might get some hits and advice.