Sherlock's Mummy
So, the only reference to Sherlock and Mycroft's mum in the BBC series is
Mycroft: And you know how it always upset Mummy
Sherlock: I upset her? Me? It wasn't me that upset her, Mycroft
John: N-no wait. Mummy? Who's Mummy?
Sherlock: Mother. Our Mother. This is my brother, Mycroft.
To me, that sounds clearly past tense. It could be short for "used to upset" or "had upset" or "continuously upset" [and I'm currently resisting to name off all the possibilities is grammar-speak :-P] ... But if it were present tense it would be, "and you know how it always upsets Mummy." And Sherlock would say, "It isn't me who upsets her, Mycroft"
Right?
Only, I just assumed from the get-go that Sherlock and Mycroft's mum was dead before this started. (In fact, it even sounds to me like the terrible Christmas dinners are a thing of the past, though I wouldn't fight really hard about that one.) And now everyone has a pet theory about her... wouldn't it be awesome if she were played by Judi Dench, etc. and I'm wondering if I'm just crazy....