Any more updates from anyone?

They're trying to bully/scare you into paying. They clearly have as much proof of this "offence" as you do that the moon is made of cheese (Wallace and Gromit A Grand Day Out doesn't count!). I'm expecting another letter. It will either be ignored, or replied with a "See you in court, then." type response. I'm sure they have to provide you with evidence for free, don't they. If they're going to rely on it in court. I'll wait for someone who's not in the same boat as you/us to reply, hopefully echoing my sentiment(!)

I would also like to know this.

So those of us who have received such letters, is this the first you've heard of any supposed offence(s)? Or *might* you have committed one? I believe mine are completely made up/not my car.

No! Also, I have never seen such unprofessional-looking letters before, although they did phone me up on my home phone and gave me another number I had to call... 01 something something something this time. My letter arrived on Sat 1st Dec. I decided to phone it and actually got through to someone. They told me there were multiple tickets dating back from february, yet they couldn't tell me where or when (same as parkingpig) also for £75. Apparently they case/tickets had been "archived" so they would have to call me back with more info..they made no attempt to try and get money off me over the phone. Yet. Anyway, before I found this thread (3rd link in google, no less) I sent a letter this morning basically stating that I had no idea what they were on about, and unless they could provide some sort of details/evidence i would be unable to assist them (I gave nothing away - the letter just had my car's make/reg but not model/colour) ... well, I basically told them where to stick it, but more diplomatically. Very much like as suggested by spuzzcake. It's going to be interesting to see what/if anything comes of this. I wish we could take these people to court for wasting our time.