A controlled parking zone (CPZ) is an area where all streets are subject to parking controls. When you enter a CPZ you will see a large entry sign like the example shown below.
The entry sign tells you the days and the hours of controls for most single yellow lines and bays within the CPZ (individual signs will show any difference). The days and hours of control vary from zone to zone, each CPZ has a code beginning CA- followed by a letter.
Double yellow lines, footways and kerb crossing areas are controlled 24 hours a day. There are also some types of parking bays in the CPZ which are reserved for specific users and may be restricted 24 hours a day.
For more information on signs and restrictions see The Highway Code