If you're new to driving on the left then take the time to get a little practice in a sidestreet first - tempers can get frayed very easily. Follow one or more of our walks or simply wander. Cars HAVE to stop if you step onto a crossing and most will stop even if you jump out into the road. Jaywalking is not an offence but natural selection can operate if you get too foolhardy. Not as good as it should be, it is possible to get around with a wheelchair or frame - however you'll need to get help with many lifts, especially in tube stations, and even then there are lots of stairs between platforms.
Many taxis have wheelchair ramps, but few buses.
Buy one from a Tube or Train station or participating newsagents, You cannot buy then once you are on the train or bus.