I too got a notification from Parking Eye, the usual £90 or £45 if paid in 15 days. I did some research and found that the best advice is to ignore the second and third letters. The third one is quite frightening, stating "Subsequent legal proceedings, and if ignored a bailiff/sheriff may attend to remove your goods."

Apparently, the police and councils are the only groups who can enforce a fine. A private parking company cannot “fine” you. They can send an invoice and hope you pay up. So my advice - simply ignore it and like me you find they move on to the next victim who is daft enough to pay.