Green Park is a good place to change from Picc to Vic or the other way
round, especially if you have luggage. BUT you must ignore the signs!
Go to the way out, go up the escalator to the ticket hall and then down
to the other line. I do this for trips to Heathrow from Euston. Can get
from Euston main line to departures at Heathrow without having to
negotiate any staircases