Maritime Safety Act 2005
26.—In a prosecution for an offence under section 23 or 24 it is a defence for the defendant to show that—
(a) he or she was acting under direct instructions from the person in command or in charge of the vessel concerned or a person in charge of him or her and it was not unreasonable in the circumstances to so act,
(b) he or she had been instructed by that person to perform a task which he or she could not reasonably perform or had not been adequately instructed to perform, or
(c) he or she took all reasonable steps to avoid the collision or incident to which the prosecution relates but due to—
(i) the nature of the vessel and the service for which she was intended, or
(ii) the weather, tidal or navigational conditions prevailing at the time of the collision or incident,
it was not possible to stop the vessel or change course in time to avoid the collision or incident and it was not reasonable to do so.