Since the law changed in October 2014, it is now the registered keepers duty to provide details of the driver. Before the law changed, you could get out of paying by claiming you didn't know who the driver was. Alas you can no longer do this.
When you park in one of these car parks, their terms and conditons are clearly displayed on boards. By parking in the car park you have entered into a contract and by overstaying, you have broken this contract.
More and more of these companies are taking motorists to court. The advice to throw the PCN in the bin means you are taking a gamble.
The last time I got one, in an Aldi car park, I did some research and found a brilliant cop out.
I wrote to them saying that one of my children, age 17, had been the driver at the time. As a person aged under 18 cannot enter into a contract, the PCN was invalid. Also, as the driver was under 18 I was not obliged to provide their details.
I never heard anymore from them