Sooner or later, somewhere in the UK, we’ll have trains with women-only coaches. It’s an idea which keeps rolling around, and though the train people complain — it’s unworkable, unenforceable — it makes no odds. It’s too seductive an idea for a progressive politician. Jeremy Corbyn was tempted by it back in 2015, and now the Scottish transport secretary, one Jenny Gilruth, is considering it.