In reply to Wallm0nkey:
Strictly speaking, since the change in the law that makes the registered keeper responsible for parking fines and costs incurred by parking (i.e. civil 'parking charge notices'), some of the parking companies HAVE taken people to court (and more than just a few test cases), and it is not impossible for them to win (although it may be that in many cases people are just not responding to court papers).
Therefore if you receive stamped court papers (unlikely), then you SHOULD respond to this, and defend your case. It is their responsibility to 'prove' that you owe them money though, and there are a variety of dubious legal arguments they use, most of which can easily be countered and some of which may be countered but I'm not sure its exactly clear yet.
However in your case it is obvious that they have no proof (and of course cannot have proof) that you were actually parked in the car park for those 10 hours, since you weren't, and even in the unlikely event that they do take you to court, you should win.
Personally, when I got a similar letter (after picking someone up from a car park, I responded once to explain why I disagreed with the charge, and made sure they had my current address, and now see no need to engage in any further correspondence unless they start court proceedings (this company does and has, but in my case they want £100 for 17 minutes parking so I am probably not a very good case). Not responding at all is probably a better way for the easily distressed by scary letters though.