I'm rewatching "Elizabeth R," (one of my all time favorites), and I'm up to the part where Essex is conducting his dreadful Irish campaign. Twice in the film, she makes a special point of saying that Robert Devereaux, Earl of Essex, may not return to London without her "express warrant." He ended up violating that order.

Why did she insist he must not return to London? Had he a reputation of dereliction of duty during war? Was there some political reason? Or was this standard procedure at the time? What if he had some good reason to want to return, such as recruitment of fresh troops? (My reading says he actually came back for political reasons: his feud with Sir Robert Cecil, his reputation was suffering because of the poor campaign, he wanted to protect his standing at court.)

As a corollary question, why was Essex's parley with O'Neill such a bad thing? If the idea was peace with Ireland, surely negotiating a treaty with O'Neill would have been useful, if not entirely what Elizabeth had hoped for.