If Mycroft wanted to know where I was headed, he wouldn't need to use a tail. [Although it will take him longer to track where Sherlock's gone through other means, especially given all the twists and turns. And the press would have been unwelcome.]

Assuming John alerted him when he left the house, I'd say we've got a solid hour before he realizes where I am. Lucky they won't be looking for you. Only waiting to see when and if I emerge. Apparently his cripple of a little brother is too much a danger to himself.

[He raises the sandwich to his mouth, take a bite out of the corner.]