They're called hop-on, hop-off because you can get off at any point, and the buses do stop near most tourist attractions, and get on the next bus from that company when you please. Your ticket is good for 24 hours in summer; 48 hours otherwise. If you're only in London for a day, buy a ticket on this bus -- it's totally worth it to see the sights.
London's Original Tour hop-on, hop-off tour buses are clean and the downstairs section is heated. Three circuits, depicted by different colors on company maps and buses, run through central London, crossing paths places like Piccadilly Circus, where you can change circuits. Ostensibly, you'll have a live guide should you choose the "yellow" line in London, although I rode the yellow line several times and never saw a guide. You'll be given headphones to listen to a taped tour, which is informative and fun, if (as is a pitfall of such things) sometimes out of synch with passing landmarks.
Grab a "Capital Connections" Original Tour bus at your hotel or near a regular bus stop after 8:45 a.m. to catch up with an Original Tour circuit bus. Buy tickets online in advance (15 GBP) or at a tour bus stop (16 GBP).
