The Driver CPC 1b test, also known as the Hazard Perception Test, is a part of the Driver Certificate of Professional Competence (CPC): 

Before starting the hazard perception test, you'll watch an instructional video explaining the process. The test itself includes 19 video clips depicting everyday road situations, each containing at least one ‘developing hazard'–with one clip containing two hazards. Points are awarded for identifying hazards as soon as they start to develop.
 

Understanding a ‘Developing Hazard'

A developing hazard requires you to take action, such as adjusting speed or direction. For example, a parked car is not initially a hazard. However, if it signals and begins to move, it becomes a developing hazard, requiring a response.
 

Scoring System

Each developing hazard can earn you up to 5 points. To score well, click as soon as you detect the hazard's onset. There's no penalty for incorrect clicks, but clicking continuously or in a pattern will result in zero points for that clip. You get only one attempt per clip, with no option to review responses. A pass requires a minimum score of 67 out of 100.
 

Test Results and Certification

After completing the test, you'll receive a letter with your result. Upon passing both parts of the theory test, you'll be issued a theory test certificate, needed for booking Driver CPC part 3a and 3b tests. This certificate is valid for 2 years, so you must pass your practical driving tests within that period, or retake the part 1 theory test.