Yes, I have been off on my travels again. It was World Book Day last week, so all the schools invite authors and illustrators in, to do talks and work with the children. I have been in schools every day for a fortnight and have had a lot of fun.
I tried to take a photo, holding up my sketchbook in the train, with the man below-left in the background, but got a right telling off by a complete stranger across the aisle from me. She said I should ask the man's permission if I was posting his photo to the internet (perhaps a good point?). Then she said I should delete all the photos I had taken of him from my phone (slight over-reaction?). Then the woman opposite her pitched in (another random stranger) saying I should not be drawing people at all unless I first gained permission.
I so rarely get a negative reaction like this (just 3 times in all the years and then only one occasion was as extreme) and get so many positive reactions, I am comfortable that she is wrong about drawing people (and asking permission to draw people would destroy it - the attention I would draw to myself would make it impossible).
Interestingly, most sketchers who post sketchbook photos with the subject behind are drawing mainly buildings. I don't think it's such a good idea on reflection, if only to avoid unnecessary conflict, so won't take photos again, even though, in this case, he would have been too far away down the carraige and too out of focus to be recognisable.