She was invited to the set by a friend (who works on the show). Here are her pictures/texts. (I'm only linking to the ones with Martin in them. To see the rest, go to
her tumblr).
I don't think the pictures are spoilery, but if you're a spoilerphobe, you probably don't want to view them (just to be safe).
Photo of Martin Martin's tea and
She brought Martin his tea What Martin is doing in a certain scene - Note: she doesn't give anything away. It's not even spoilery.
Martin and Ben sitting in their sit chairs Martin on the set (taking a break?) and
here's another one Martin and Ben getting ready for a scene Ben handing Martin Sherlock's scarf Getting ready for a scene Martin’s kids just ran onto the set to give him a cuddle and he keeps waving at them. My ovaries.
Text about Martin's kids being on set ETA: I found some more photos.
http://cumberbatchweb.tumblr.com/archive/ Click the pictures to view them at full size.