h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Many people are unaware of the availability of cheaper train tickets if you book early.

The details depend on the train and the route but savings of almost 50% can be made by booking tickets over either the phone or internet. Commonly, you have to book either 7 or 3 days in advance. Apex or Super Advance Saver are example names for some of these ticket types.

The drawback is that you have to specify the exact trains on which you travel and the tickets are invalid on any other ones. Tickets can sometimes be altered before the date of travel, although usually for a small charge. Also, there are only a limited number of these tickets available, so book early!