Chiltern class 165 stock has a useful between-seat space in its quiet zone - always assuming it's not full of Brompton from further out. On class 168 stock (on the rare occasions I have to use it) it gets left in the lobby. On the underground it sits next to my seat. When I used to use SWT regularly I either had it next to my seat (on the suburban trains) or sat right next to the lobby (on the long-distance train). I've managed 21 years without a theft, and I've never carried a lock of any kind on my Brompton, so I must be doing something right.