Anything done by a person (A) in the course of A's employment must be treated as also done by the employer.
Anything done by an agent for a principal, with the authority of the principal, must be treated as also done by the principal.
It does not matter whether that thing is done with the employer's or principal's knowledge or approval.
In proceedings against A's employer (B) in respect of anything alleged to have been done by A in the course of A's employment it is a defence for B to show that B took all reasonable steps to prevent A—
from doing that thing, or
from doing anything of that description.
This section does not apply to offences under this Act (other than offences under Part 12 (disabled persons: transport)).