Just a thought, a PPC writes with a speculative invoice, I was not driving so I speak to the driver who denies all knowledge of any supposed contract, and states that I am not to pass his details on to a private company, otherwise he will sue me, quotes data protection, where do I stand?

He would have zero chance in court.

Disclosure for the purpose of legal proceedings, including prospective legal proceedings is exempt from the DPA.

It leaves him with three options :

1 He agrees to indemnify you from all costs if/when the parking company brings a claim including a reasonable sum for your wasted time.
2 You tell the parking company that he won't let you identify him without a court order. The parking company can add the cost of the order when they claim against him.
3 He stops acting like a prat.