The laws of physics make it impossible for a car to stop dead. Similarly it is impossible for you to instantly react and apply the brakes. (See braking/thinking distances in the Highway Code). This is why you need to anticipate what might happen next and plan a course of action rather than wait until it actually happens. Although the examiner is not requiring you to do this as well as an experienced driver he or she will expect you to anticipate and act upon the more common hazards that occur.
What the examiner is looking for
The examiner is checking that you
Take every opportunity to look, see and act on what's happening well ahead and around you
Particularly recognise the potential hazards that vulnerable road users can present and act accordingly
Use the MSM routine on approach to any potential hazards
Act upon any potential hazards by adjusting speed or position or both
Slow down and stop where it becomes necessary to avoid dangers.
Driving faults recorded
Not anticipating that pedestrians are about to cross the road at any time.
Not giving way to pedestrians at junctions or pedestrian crossings.
Not anticipating that cyclists may be passing on the left or right.
Not anticipating that cyclists are about to make a change of direction.
Not anticipating or showing awareness of direction signals given by other drivers.
Not anticipating or showing awareness of vehicles displaying hazard flashers.
Not anticipating or showing awareness of vehicles reversing lights.
Not anticipating or showing awareness of brake lights on other vehicles.
Not anticipating the actions of other drivers changing speed or direction.