... as long as the employee carries out the written instructions of the employer, as far as I understand it, they are protected.
Vicarious Liability - a Legal delegation of Responsibility.
Trouble is, page one in the book is still something like "Nothing in these instructions shall prevent an operator using their own judgement and doing more than required" (words to that effect). It's basically an all care no responsibility disclaimer from the rule writers. The way it was explained to me was if the rules were stupid or inadequate you has a duty of care to realize that and do more.
I've even has an email from my then manager saying a clear cut well defined procedure was in his opinion not ideal, and maybe we should think carefully before using it. Spineless so and so wouldn't actually commit himself one way or the other though!