Parking restrictions can be enforced by several different authorities in several different ways.
Only used on-street. Police officers and police-employed Traffic Wardens can issue Fixed Penalty Notices. If not paid, the motorist can be prosecuted in a magistrate’s court for original parking offence. Appeal is by not paying, and putting a defence in court if prosecuted. Some can include penalty points on a driving licence – this is the only type of parking ticket that can. This is not commonly used any more in most areas.
Used on-street and on car parks. Councils with Civil Enforcement employ (or contract out the employment of) Civil Enforcement Officers, who can issue Penalty Charge Notices. These are a special civil process, that if not paid can be registered as debt and enforced by bailiffs. There is an appeals process, appealing first to the council, then to an independent adjudicator. The adjudicator is set by government regulation, not chosen by the council. The registered keeper is liable, regardless of who was driving, with an exemption for hire cars (the hirer may be held liable).
PCNs are issued with codes and descriptions that are usually self-explanatory, but a handful have wording that isn’t obvious – “Parked in a restricted street during prescribed hours” generally means a yellow line. Here’s a list with most of these codes, and what they mean.
Civil Enforcement Officers (and other council officers) can issue Fixed Penalty Notices for non-parking offences (such as littering) in some areas.
Council ECN or SCN
Used only on car parks or designated parking places. Councils used Excess Charge Notices or Standard Charge Notices before PCNs were introduced in The Road Traffic Act 1991; some councils still use them if they have not applied for Civil Enforcement. They work in the same way as Fixed Penalty Notices; councils will usually offer an internal appeals process, but there is not a legal requirement to do so.
Used only on private land. Private companies use a variety of names for their notices, often “Parking Charge Notice” or similar. These have an appeals process similar to council PCNs, including the appeal to an independent adjudicator (although a different service is used). These use contract law – by parking, you enter into the contract offered on the signs. Common advice used to be to ignore this type of ticket, as the company typically had no proof the keeper (who they would pursue) was the driver that entered into the contract; The Protection of Freedoms Act 2012 enabled private companies to hold the registered keeper liable regardless of who was driving making this advice outdated. Companies may sue through the civil court process to recover unpaid notices.
Some councils contract out enforcement to private companies – in this case employees of the private companies will issue council PCNs, including on-street, but the details on the notice will be that of the local authority.