If the penalty is not paid within 28 days of the date of the Penalty Charge Notice, the enforcement authority may issue a Notice to Owner (Parking) or an Enforcement Notice (bus lane) to the person appearing to them to be the owner of the vehicle.
The owner is usually, but not always, liable for the Penalty Charge Notice, whoever was driving.
The Notice to Owner/Enforcement Notice will usually be served by post. The person to whom it has been sent then has 28 days, beginning with the date of service of the notice (ordinarily when it arrived at the address to which it was posted) to:
Pay the penalty charge;
Make formal representations to the enforcement authority explaining why they think they should not have to pay the penalty.
If you wish to do this, you must still write back to the enforcement authority at this stage, even if you have made a written challenge following the issue of the Penalty Charge Notice at the scene.
Further details of the enforcement process for each specific contravention type can be found on the pages for Parking and Traffic Adjudicators