I am struggling to see what the problem is here. As I understand, you want to take your baby out for the day - a journey which involves being on a train with available changing facilities. As long as you feel fit enough to go, then just make sure you have what you need with you and enjoy your day.
What people are likely to lash out at someone with a young baby?
Maybe I am sheltered in that I don't live in or near London, but I can't see that happening somehow.
Sounds to me that he has some control issues - he is right, she may need feeding or changing, babies don't always work to a plan! But I still don't see how that is a problem. If you were hanging out the window of a train in central Mumbai maybe ;o).
It is actually easier to travel with them when they are little like that than when they get older and more restless - a four week old will sleep most of the time.