Grant Urismo is right, it costs a lot !!
The actual legal mechanism available to both councils and appellants in PCN cases is called Judicial Review, and means a High Court judge assess the decision made by the adjudicator and decides if it was lawful or not. Normally if a council goes to JR, it is agreed with the High Court before the hearing takes place that the original appellant will not have to pay the PCN, the JR is for future cases. As said, these cases can end up costing a fortune. Transport for London took London Tribunals to court concerning Red Route parking decisions and won, for all the good it did them. They employed a KC !