Board Thread:Series 5 Discussion/@comment-6905051-20130327100352/@comment-5674726-20130331001744

''Why Merlin always accompanied Arthur on every mission is as much a miracle as the fact that Arthur always went on missions himself when he was king already. There was a reason why Uther stayed in Camelot and sent his men. A kingdom without a king is as worthless as a door without a door handle.''

It made no sense for Merlin to accompany Arthur whenever he left the castle, be it for a hunting trip or for a dangerous mission. If Arthur was supposed to be away for at least a few days, then maybe he might bring his servant to attend to him but there's no reason why he would want to have Merlin tagging along with him on routine patrols. He certainly wasn't bringing Merlin along for the ride because he thought that he would be an asset in combat. It's not like Merlin didn't have a mountain of chores to keep him occupied in Camelot and even Arthur would have to see that it's unreasonable to condemn him as a "lazy idiot" if he's constantly dragging him away from his duties in the castle for no better reason than to tag along and be told how useless he was.

Short of Merlin using magic to implant a suggestion in Arthur's mind that he should bring him everywhere, I can't see why Arthur wouldn't leave him behind.