It's not exactly the easiest tour in London to get on. You have to contact your MP to book, and then wait around 6 months for the date to arrive. You have to go through better than airport style security to get into the building, there is a ban on photography, and you have to climb up all 334 steps up the clock tower.
Today I visited Big Ben!
My legs were like jelly at the top, but watching and hearing the bells chime 3pm was oh so worth all the effort involved!
I can't recommend the tour highly enough, with just a small group of 7 people, we saw the clock and bell mechanism, got to touch the back of all four clock faces and of course got to watch Big Ben strike the hour!
Also as a little bonus the tour guide let me have a look around Westminster Hall by myself after the tour.
Contact your MP now and book yourself a place. You won't regret it.
As I couldn't take any photos inside, I spent an hour walking around the Houses of Parliament after the tour taking a few snaps...