You did what is called a "driveaway", and before the Traffic Management Act 2004, you'd have got away with it, but this was dealt with under this Act, and allows them to serve a postal PCN to the owner, (who of course may not be the driver). Under the legislation, PCNs are the responsibility of the owner to pay or appeal.
Please post a GSV link to the exact location, telling us where the car was parked, how long you were there, and why you were there. This is very important information for appealing possibilities.