Accident and emergency departments have to deal with a huge variety of injuries and situations, not all of them strictly medical. They often have to do so under very trying conditions, at all hours of the day and night. Despite those often difficult situations (and often difficult patients), the clinicians that staff A+E are subject to exactly the same legal duty as in other medical environments- that is, to deal with the problems presented to them in line with the standard of reasonable clinicians.
In the nature of their work, A+E staff often face emergencies- and the medical actions taken in emergencies can often be justified when in a calmer situation with the luxury of time to reflect and choose, they might not be the actions of choice.
The law does not presume to lay down which of several possible course of medical action is to be preferred- provided what was done would be supported by a sufficiently sizeable number of reasonable clinicians, then the law will not interfere- even if there is dispute within the medical profession about one or the other course of action.
A+E clinicians are often subject to enormous pressures of time and volume of work and in much the same way, not all cases of delay or choosing one course of action over another, will necessarily be negligent. On the other hand, it is also settled law that clinicians, even under the stresses of emergencies, or under pressure, cannot simply refuse to treat a patient who reasonably needs treatment; nor should they make assumptions which are not justified by the medical facts.