Torchwood wasn’t well liked by the Cardiff heddlu, which was understandable. Trouble was, they ran roughshod over everyone from uniformed coppers on the beat to inspectors and crime scene people.
It was easy to think that Jack and his team should be more polite, but in an emergency there was seldom time to ask people to leave, and wait while they made up their minds. In life-or-death situations, if sending the police packing saved them from attack by something they weren’t prepared to deal with… Well, Jack would rather have them alive and hating him than dead.
Simple as that.