If clamper has no license to clamp, he is breaking the law you can do what you like, it is a GIFT from him to you, you could also seek costs from HIM if not licensed.
If he is licensed and appropriate signs were displayed etc then it is criminal damage.
As it has been a year you can assume he was NOT licensed, your freind has no need to worry as said too long ago as it is over six months, they woulkd have been spoken to well before the end of this six months, NO CPS would run it and no court would accept it.
You are quite at liberty to remove by ANY means an illegal clamp, if it becomes damaged, they would have to sue you for damages, which would not happen in a months of sundays.
tabetha