Hi there, I commute every day to central London and have found that simply targeting fit, healthy young men and asking for their seat works a treat. The other morning, I saw a pregnant lady get on one stop, look around in vain and remain standing while everyone read their papers. I thought of asking the person beside me to let the lady sit down but she got a seat pretty quickly at the next stop. I guess my point is that if you don't ask, you don't get :) I genuinely believe people are fine and it would be an absolute w**ker who wouldn't let you take their seat if you asked.