Driving Examiner Guidance: Signals
The examiner should satisfy himself that the candidate reacts promptly and correctly to traffic signals and signs and to signals given by the police, authorised traffic controllers and other road users.
The candidate should be fully aware of their responsibilities at pedestrian crossings, and act accordingly.
Methods of Signalling:
Candidates normally signal by direction indicator but may, if they wish, additionally signal by arm. Signals should be assessed on whether necessary and appropriate signals are given in good time, and indicators cancelled afterwards.
In the case of a disabled driver it will usually be apparent whether they are physically capable of signalling by indicator and arm. However, if the examiner can only satisfy himself about this by observing the candidate giving signals whilst actually driving, they should specifically ask the candidate to signal by indicator or arm as appropriate, but only for as long as is necessary to determine whether or not they should be restricted to driving vehicles fitted with direction indicators and stop lamps.
The above is taken from The Driving Examiners Manual.
Where appropriate it has been reformatted and edited so it only refers to the driving of ordinary cars (class b).