For the most part, people will typically do everything they can to not park illegally but there are certain cases that feel appropriate to take a measured risk. Unfortunately, these can often lead to a public parking ticket which will usually be issued in the form of a Penalty Charge Notice (PCN). A PCN can either be left on your vehicle or even posted to you, if caught via CCTV. A PCN is not something to ignore and the sooner you handle it the better.
When you pay a PCN within 14 days of the issued charge you can often get it reduced by 50%, which means a £70 charge, will only be £35. Not paying within the initial fortnight will mean you will have to pay the full amount within 56 days. After this, if left unpaid, the fine could be increased a further 50% which would take the fine up to £105.
If you feel a PCN was given without warrant, do not ignore it, as you can challenge a PCN within 28 days of issuance but these could possibly still get rejected. The most important thing is that you simply deal with a PCN as soon as possible to avoid further penalty.