I was told that if your train is more than 10 mins delayed, you can reclaim your money back. However, this is not stricly true. Firstly it depends on which compant is running the train. Virgin will give you your money back (i think), but for CrossCountry, it has to be 30 mins delayed, and you'll get 50% of your money back. It has to be 60 mins delayed or more to get the whole thing back. 60 mins! A whole hour delayed before they even consider giving you your money back! Ridiculous.
However, even if it is this bad, i would recommend everyone to attempt to claim, whatever their journey, if it is delayed. The more people who try might make them realise they need to do something about the late trains.