How to bypass lines at London sights

Yes the travel passes purchased through National Rail, NOT Transport for London, will qualify you for the 2 for 1 deals. You do have to buy admission at the various sites since you have to show the travel card to get the discount. As the others have said the lines are not bad, especially if you show up first thing in the morning. Even when there are lines, you're not talking Disney ride length waits, so no Fast Passes. :-) If you know where you want to go, it helps to print the vouchers ahead of time; that you can do online. Enjoy your trip!

I haven't heard of Fast Track, so I'm not sure how to help you, except to say that at least for the Tower, just get there when it opens and you won't have a long line. We never really felt that we ever waited very long at any UK site. You can also save some money by buying Travel Passes from a National Rail Station. They are good on the Tube in the designated zones (zones 1 & 2 are usually enough for tourists), and of Dockland Light Rail. They allow you to use the Days Out 2-for-1 deals (see this website http://www.daysoutguide.co.uk/2for1-london ) Just print out the vouchers you plan to use before you go because the rail stations sometimes run out of the booklets. The passes come in 1 day and 7 day amounts. If you are going to get the 7 day cards, bring a passport sized photo so they can make the required free ID card when you buy the pass.

Annie which sites are you most concerned about lines at? Since most museums are free I have never really encountered any lines at them myself.

So just to clarify, if I buy a Travel card (instead of an Oyster Pass), I will get 2 for 1 vouchers, but I do have to redeem them at the sight and line up for the tickets. So there are no 2 for 1 offers that I can purchase online then.

We want to see the Tower of London, Westminster, St. Paul's, Thames cruise, Hop On/Off double-decker tours maybe Windsor, maybe London Eye. Also the free sights--British Museum, British Library, etc.

I was in London last week, hight of vacation summer season and the only place we had a line to wait was Westminster Abby. Tower took like 5 minutes, Abby maybe 15- 20 minutes. Both places we did not arrive at opening but probably an hour later, so if you went earlier you may have no wait.

We were in London 2 weeks ago. I had ordered the Tower tickets on line to be picked up there, so I had to stand in a short line to get the tickets I had ordered. What we should have done is while I was in the line to get the tickets have my husband stand in the entrance line. We didn't do that so the line was very long (we were there 30 minutes before it opened); however, I will have to say that the line went very fast, and we went right to the jewels when we got in - no problem. When we left from the jewels, the wait to get in was 45 minutes. We also got to Westminster the next day 30 minutes before it opened - line was already very long, but things seem to move quickly. No problem at all. As was said, this is top tourist season - when we've gone in May or September there have been virtually no lines.

Was in London 2 weeks ago. If you get use one of those Hop on Hop off bus tours there are people on the street usually selling tickets to the Tower right off the bus, no waiting.
Do be warned though-we did not go to Madame Tussauds,and the wait was extremely long! Down the block! At everything we did, we waited no more than 20 minutes at most, even during weekends.