Tour buses., London

Tourist bus. Yes, very touristy but not a bad way of seeing the city. Most of these have an open top deck and some kind of commentary service. You should be able to pay once and then hop on and off buses if you want to stop somewhere. They are available all over the West End.

'Look kids, it's Big Ben and Parliment' I tried like hell to find the rotary Chevy Chase was stuck at all day in National Lampoons European Vacation and get this shot from here -but I ran out of time and light.
If you have never been, and wanted to get a 'slightly guided' run around the city they have double-decker busses that run 4 or 5 different routes around. They are only like 10 or 15 pounds for an 'all-day pass'.
They make great transportation about and you can hop on or off at any time if you want to walk around or go see any attractions. They keep running the same routes so you can usually catch another within 20 minutes...no too bad!

Making us of the hop-on, hop-off busses is a great way to see the city and learn about the various places that you pass. Valid for 24 hours, it is the best way to experience the city

Hop on the red double decker London Sight-Seeing Bus and see Trafalgar Square, Piccadily Circus, without any hassle. Hop off your next destination. Great introduction to London on a fine weather day.

When we weren't "on our own steam" as Harriet (our guide throughout the trip who happens to by British) said, we toured about in a bus allocated for our tour group.

These double decker tour buses are everywhere. I admit they are a bit slow, but if you have all the time in the world, they're ok.