I just listened to the radio 4 show that was linked earlier in the thread and heard Crossley himself say:
"all we're doing is putting them on notice that their IP address has been utilised, we offer a compromise, they're under no obligtion to pay it, but if they ignore us we will take further action"
What does this mean? That the letter is basically a warning that my connection is now being watched, pay up if you did it, if you didn't just let us know and we'll forget about it??? That sounded quite confusing.