There are dozens of booking agencies in London, including some based in major hotels. You can also call the theater box office directly. Credit card and telephone bookings are always accepted. If you just want to see a show, and don't particularly care which one, visit Leicester Square's Half-Price Ticket Booth. The booth sells all tickets at half price, plus a service charge of about 1 pound.
Tickets are for performances on day of purchase only.
Tours generally cost 3 to 4 pounds and take around two hours.