Dear Lady on the Train,
It doesn't matter how loudly and frequently you complain about gentlemen commuters not giving you a seat, the very fact that you've mentioned it has immediately glued their buttocks to the upholstery. Please be aware that commuters are creatures of habit. They have their bit of their carriage and their routine with their newspaper / ipod / blackberry / snoring and after a long day of pontificating and many years of practice will stick to this routine through hell or high water. A train has to be stuck stationary for a minimum of two hours before a commuter will speak to a fellow commuter whom he sees every single day. That is how rigorously anything which doesn't comply with the routine is ignored. He can quite easily ignore you for the usual 45 minute journey.
A commuter feels justified in this possessiveness of his seat when he has paid three and a half grand for it and tailored his day to ensure he gets to the station early enough to claim it. You with your lowly off-peak return, scrambling on at London Bridge, are way down in the pecking order.
Also, if the conductor kindly tells you there are seats further forward in the train, take his advice and use them instead of yabbering on when I am trying to work. Unless you would like to take my exam for me next week?
Lastly, complaining that you are 72 and your travelling companion is pregnant is not going to encourage gallantry, especially when you clearly are not 72 and your travelling companion is carrying her belongings in a bag marked 'HM Prison Service'.
A Lady Commuter.