It was taken by Mags Halliday who's pretty certain it was Bob Crow. Why? Two reasons a) "He was wearing an RMT badge" and b) He was sitting "legs apart so that he took up both seats, though there were people standing".
Well spotted Mags, who said "After all these years semi-working in London I finally get a celeb spot on my last trip pre-baby. Although it tells you a lot that I recognise a union leader over an actor or musician".