The law has changed but not the basic principle of whether they can penalise you. The law is that the only contract that exists is between the driver at the time of the incident and the landowner. So it used to be that they issued the penalty to the owner but, to be enforceable, they had to be sure who was driving at that time. As there was no legal responsibilty for the owner to inform the parking company who was driving then by ignoring it, you were generally safe and the handful of prosecutions were only against people who were daft enough to admit they were the driver.
The law changed when they outlawed clamping so that the registered keeper of the car became responsible, regardless of who was driving. But the basic principle, that the landowner can only claim for the actual loss they've suffered, is still the same as I understand it. So the chances of a successful prosecution are still low.