The train pulls into the station and people surge towards it. As soon as I get on my heart sinks. Every seat is taken. I push through the door at the end of the carriage; it's a dead end. But it’s also a breathing space, which is more than anyone has in the over-crowded carriage I just left. It’s cold here, peaceful. I sit on my bag and stare out the window as London slips away. This will be a very long three hours.

I’ve been sitting on my own for about five minutes when a girl with dreadlocks pushes her way through the door…