Anger coursed through his veins.. not at John, but at Mycroft. He took a moment before composing his message so it wouldn't come out wrong.

This will be dealt with. Don't worry about it any more. He will not darken our door again. I will ensure it.

To be honest, he really had no way to keep Mycroft from his flat, but he would find a way to make it as inhospitable as possible if he ever did come by again.