I have one from last year for parking in a KFC car park for 10 mins (not exaggerating the times are on the ticket) they wanted £75 within 2 weeks or it would go to £150.
I ignored the second letter requesting £150 and then received a third letter saying if I don't pay they will hand over to bailiffs and 'could' receive an even larger fine.
A lett from 'Newlyn' bailiffs came through (which i later found out is owned, or part of the company that sent the original ticket) and they wanted £238.
I rang them up and asked about how I appeal and they said they would put it on hold for 300 days. This period expired sometime in august and I received a reminder that I owe them £238 and that if I didn't pay they said they 'may' register with the court which 'could' result it a larger fine.
Before they can even send the bailiffs out they need to get the case approved/accepted or whatever by the courts AFTER registering it. Even then I think they have to have a valid case to be able to register it (mighty elvi could confirm this).
So I ignored that letter because they were clearly trying to use a bunch of scare tactics. I was prepared to go to court.
They then sent out a big scary FINAL WARNING letter OOOOOO scary. Saying that if I did not pay up i could face further costs and legal action bla bla bla.
I have ignored that and I haven't heard anything for about 2 months. Ignore them unless its a council ticket. If you do want to contact them don't make any claims (i.e something you might have seen on a sign) without real evidence, don't be rude, threatening or sarcastic and only contact them if they contact you first.
Remember, its just a scam and an utter load of bullsh!t.
Also ask them to prove it was you.