In Sherlock S04E03 we see Mycroft disguised as a fisherman along with John Watson to let Sherlock (impersonating a security official) meet Eurus. Time and again in this episode as well as the previous ones, it has been clearly mentioned that Mycroft holds a respectable position in the government; infact he himself is the British Government. Without the direct orders of Mycroft, no one is allowed to diagnose Eurus or even talk to her.
So couldn't Mycroft just order the Sherrinford authorities to let Sherlock meet Eurus.
Why did they undertake so much trouble for the meeting?