The law has changed in that the Parking company can now pursue the registered keeper of the vehicle rather than having to prove who the driver was at the time.
Regardless their ticket (sorry invoice) is still no more valid than it ever was and my advise would be to simply ignore.
There seem to have been a few cases launched by Parking Eye in the courts but if you look at the details, then these cases seem to be costing Parking Eye far more in legal fees than they ever get back in tickets.
For instance their was a case recently in Manchester that went to court. The driver had parked twice in a paid car park without paying. Despite Parking Eye claiming legal costs of around £4,500 (having 4 solicitors working on the case) the judge awarded damages in Parking Eye's favour of just £15 (the same £15 it would have cost the guy to pay for parking in the first place). In addition the driver had to pay Parking Eye legal costs of just £95.
Clearly taking drivers to court is not a sustainable business model for Parking Eye and I suspect that these very few cases that they are trying to take to court are meant for pure publicity - to try and scare the majority into paying up. Judges generally take quite a dim view of the tactics used by these parking companies in trying to extract money from descent people, particularly when exorbitant legal fees and charges are involved. These parking company's don't really have any other way of getting money out of people without trying to put the 'fear of god' into them.
Unless it's a valid and proper court summons just ignore and see what happens. If it goes to court (unlikely) and if they find in Parking Eye's favour (again unlikely) then it will cost them far, far more than it will ever cost you. In the case above £95 well spent I would say