You can buy tickets on the day of travel. For many day trips up to a hundred miles from London the best buy is a cheap day return, valid only that day, and only on trains that leave London after 0930 on weekdays, but any time at weekends. In principle you cannot break your journey, but in practice I do, often, and ticket inspectors just smile. If, like me, you are aged 60 or over you can buy a senior railcard, if under 60 a Network railcard. Each costs twenty pounds and gives you a third off these cheap day returns. For detail on both of these please see http://www.atoc.org/railcards/railcard_main.htm
For longer day trips, such as Bath, Chester, Stratford or York the most expensive is the full return fare, bought any time, valid a long time. It lets you break your journey, but I doubt you want to do that on such 2 or 3 hour trips. What I do is phone in London 0845 7 48 49 50, and tell the helpful people at the other end my plans, and ask what cheap tickets are on offer by advance purchase, with what limits on early morning departures. I take notes, and go to any big railway station in London to book my trips. The best office for this is on the street below Cannon Street station, Monday to Friday, nine to five. Roughly, cheapest is SuperApex, then Apex, then SuperSaver, and cheapest is Saver - but there are more offers still, with even odder names, for example, Value Fourteen. Mostly, you cannot break your journey, and mostly they are valid for a certain 3 days, a certain day, or even a certain pair of trains. You can buy the whole set at one go: they date them for your choice of days. If you miss a train named on an Apex ticket in principle you pay the whole single second class fare, but in practice an explanation and apology to the conductor usually wins a kind reply. I expect that an American accent helps, too.
Let's take, for example, the familiar task of booking a train to Edinburgh from London. You can take the cost down if you phone from the States in English office hours to ++ 44 845 7 225 225, Great Northern, and buy a bargain saver ticket at 25 pounds single or 36 pounds return. The company hold a stock of such tickets, and when they sell out sell no more. You can book from six weeks to ten days ahead of travel, but of course the earlier the better. Once made, the booking is unalterable to another train, much like an Easyjet booking.
You can save a hotel bill on the Edinburgh trip if you take a sleeper overnight, at 40 pounds return or 30 pounds single in a 2-berth single-sex compartment. For this Apex ticket you book as soon as you can on ++44 845 7 550 033, Caledonian Sleeper. You might go one way in bed and the other by day to see from the train the sights at York, Durham and Berwick upon Tweed. Board at London Euston at 2300 (perhaps after a curry in nearby Drummond Street), tell the conductor you want a long night, no morning drink, and a late knocking-up call, leave at 2340, reach Edinburgh 0717, stay asleep, quit the train at the last possible moment, 0800. Take a lift to the footbridge, and take a taxi to your hotel. Do look out as you quit the station, to see one of Europe's finest arrival townscapes, New Town to your right, Old Town to your left. Going south, board at 2330 (or as early as the rules allow), have same serious talk with the conductor, arrive 0700, stay asleep, leave the train 0800. Now the tricky bit. Breakfast in Euston station is poor. So look for the motor ramp away from the station up from the platform, walk up to the blocks of apartments on Barnaby Street. Turn right, go to the main road called Eversholt Street. Turn left, cross the road, and there is a workers café, run by Algerians, spotless, with good breakfast. After that, from the same side of the road take a bus southbound to Holborn, the Strand and Waterloo, for a change of bus to your hotel.
For a good but expensive breakfast, from the sleeper you can take your luggage up in the lift to the footbridge, turn left to the few steps up to Market Street, and choose your entry. You can turn left there, walk your bags twenty yards and look across the street for the minor door, the goods entrance to the Carlton Hotel, an old five star hotel. Or you can simply cross the road to the goods entrance to the Scotsman Hotel. You buzz the intercom there, and take the lift to the Bridge restaurant on level one of the Carlton Hotel or the third floor of the Scotsman. At the Scotsman a full Scottish breakfast costs £16.50 per person and continental breakfast is £13.50 per person, and the Carlton costs more again.
Webmaster note: Ben Haines died in March of 2007. I am proud to have hosted his writing on the VRW website, and will continue to keep these characteristically helpful and joyful essays online for all to enjoy, as a small memorial of this kindly, intrepid man who shared so much with us over the years.