Transit for London, the governing body of the London Transit System, has made a tremendous investment in making trains and busses accessible and easy to use for all. Stations have been refurbished and new trains and busses have been purchased that provide space for wheelchairs. This is especially evident in East London, where the Olympics and Paralympics will be held in the summer of 2012. Many lines and stations are still under refurbishment in hopes of having a smooth transportation venue for the Games.
Despite these efforts, anyone traveling to London should be aware that by no means is this a 100% solution. We will try here to provide details to make transit in the metropolitan area helpful by providing the good, the bad, and the ugly.
The Bus System
The bus fleet has been upgraded, and we are happy to report that there are ramps and priority spaces on all of the busses. Travelers on busses must also know that not all busses stop at all stops. You must flag the bus down, or it may whiz right past you. Once it has stopped, the driver should keep the front door closed and open the rear door and lower the ramp if you are in a wheelchair. The space for a wheelchair is often shared with baby buggies, but you have priority, and the bus driver should advocate for you and request that the buggy be removed if it is taking up too much space. The space itself is a bit tight. Busses cannot take a wheelchair more than 27 inches (70cm) wide and 47 inches (120cm) in length. There is also an inconvenient pole right in the middle of the space with a stop request button on it.
The Underground and Docklands Light Rail (DLR)
Many enhancements have been made and are ongoing. Visual and audio alerts can be found in all of the stations that warn of upcoming trains and notices about outages, induction loops are at some of the station ticket offices for hearing impaired travelers, bumps have been installed on platforms so that travelers with sight impairments know where they are in relation to the edge of the platform, elevators/lifts have been installed in many stations that have braille, raised signage, and audio cues, and some of the stations have been outfitted with plexiglass barriers with doors that open when a train is stopped and lined up with the doors. Most trains have audio alerts to warn passengers of upcoming stations, and a growing number have visual alerts, as well. We also found attendants on the platforms and in the stations no matter where we went. While this is fabulous progress, there are still a few other things to consider.
Mind the Gap
Anyone who has ridden the Underground, otherwise known as the "Tube" knows that this phrase is used at every single station to warn travelers of a sometimes large gap between the train's threshold and the platform. This could mean a difference of up to a foot high, and several inches across. I wish I could say that this is completely removed from the system. Unfortunately, it is not, and you will find that the great majority of stations in Central London still have them.

Typical step free access to platform - 6 - 12" height difference at platform
Typical step free access to train - Less than 3 inch difference at platform, up to 2 inch difference in width

New doors that block access to the track when a train is not in the station
Read the Fine Print
Transit for London has created a way to alert the traveler as to whether or not they will encounter a gap that would require assistance for boarding. When looking at their Tube maps, there are two designators with wheelchair symbols.
White circle with a wheelchair: This symbol means that there is step free access to the platform. It does not mean that the gap between the train and platform has been removed. In almost all cases, we found height differences over six inches high, and width of approximately two inches.
Blue circle with a wheelchair: This symbol means that there is step free access to the train. There will be lifts (elevators), to the platform, and the vertical distance between the platform and train is less than two inches. The width will also be less than two inches. Thing to note: Just because a station is designated as a "Blue" station, doesn't mean that ALL of the platforms are step free. For example, at Stratford Station, the Jubilee line was step free, but on the Central Line, Platform Three had a significant step up. If you want to get really scientific and know exactly what each station's gap measurement is, you can get a map at http://www.tfl.gov.uk/assets/downloads/step-free-tube-guide-map.pdf.
Crowded Busses and Trains
Travel during traditional rush hours in the morning and the afternoon, and Saturday afternoons in Central London can prove to be quite a challenge whether or not one has a disability. The vehicles are packed beyond reasonableness, and it could be difficult to get on. People just do not move, regardless of who/what is trying to board. There are priority areas, but the paths and areas are so filled up with people packed as tight as sardines that you won't be able to navigate to get to them. You can ask for assistance, but know that the attendants will not ask anyone to get off the vehicle. They will attempt to shift people, but when the train/bus is so tight, there may be nowhere to go. Consider traveling during off hours if you are a tourist.

Boats
If you wish to enjoy transport on the River Thames, the Thames Clipper operates at ports throughout Greenwich and Central London. A word of caution: while the boats are very accessible and can accommodate any size wheelchair, the ramps can be VERY steep. Also, we found that the Embankment Pier was a bit tricky to navigate to find an elevator to go up to bridge level. It is around the corner of Waterloo, by the way, but it wasn't marked well, so there was a bit of wandering before we found it.

Time and Money Saving Tips
Wheelchair users ride free on all public transportation. People with other disabilities who live in London can apply for a Freedom Pass that allows free passage.
If you are not disabled, and plan to use public transportation nearly exclusively and will be riding at least three vehicles a day, it is advisable that you get a Travelcard. They are sold in one, three and seven day increments. You will need to know what "zones" you will be traveling in. "Zones" are areas of the city, with Zone One being the very center of London, working out to Zone 6, which is Heathrow Airport. When you move to another zone, your fare increases. Look at a map and figure out where you think you will be going (most people don't go much beyond Zone Three, but it really depends on what you wish to do. You can then purchase a Travelcard for those zones. You will be given an Oyster Card, and charged an additional deposit of five pounds that you get back when you return it at the end of your stay. This card allows you to place it up against a reader for access to trains and busses. It also gives you reduced fares for Boat passage.
Pay as You Go - Oyster Card
You can also pay a deposit for an Oyster Card and place a set amount on the card. The amount you travel will be deducted from the card at a reduced rate from cash fare for each ticket.
Again, we cannot stress how much improvement we have seen in the last few years. Staff training and awareness is definitely heightened, and we are confident that as more travelers with disabilities visit, the economic benefits of catering to the needs of everyone will continue the investment in the future.
For more information on Transport for London Accessibility, including additional information on Dial A Ride, Minicabs, government subsidies, and other valuable tips, go to: http://www.tfl.gov.uk/gettingaround/transportaccessibility/1167.aspx