If you're on a tight budget, long-distance buses (coaches) are nearly always the cheapest way to get around, although they're also the slowest – sometimes by a considerable margin. Many towns have separate stations for local buses and long-distance coaches; make sure you go to the right one!
National Express (www.nationalexpress.com) The main coach operator, with a wide network and frequent services between main centres. Fares vary: they're cheaper if you book in advance and travel at quieter times, and more expensive if you buy your ticket on the spot and it's Friday afternoon. As a guide, a 200-mile trip (eg London to York) will cost £15 to £25 if you book a few days in advance.
Megabus (www.megabus.com) Operates a budget coach service serving more than 100 destinations around the country. Go at a quiet time, book early and your ticket will be very cheap. Book later, for a busy time and… You get the picture.
National Express offers discount passes to full-time students and under-26s, called Young Persons Coachcards. They cost £12.50 and give you 30% off standard adult fares. Also available are coachcards for people aged over 60, families and disabled travellers.
For non-UK citizens, National Express offers Skimmer passes, allowing unlimited travel for seven/14/28 days (£69/119/199). You don't need to book journeys in advance: if the coach has a spare seat, you can take it.