National Express are about as evil as you can get.  If you lose your ticket, even if you have proof of purchase, you have to buy another.

Their argument:  If you bought something in a shop and lost it, the shop would not have to replace what you lost.

Our argument:  You have not bought "something".  You've bought the right to be on a train.  They cannot sell this right to you twice.  If they do, they must refund the first purchase.