The tube system in London is great for travellers trying to save little dough. However, the accessibility for mobility impaired persons is limited…
Not all stations have lifts (elevators). Not all stations have escalators. You can do a quick online search or check a tube guide to see if the station is disability friendly. Take the guide recommendations with a grain of salt. We got caught out with our chair and an escalator only station.
Another issue is that the tube is used by A LOT of people. The number of people getting on or off the tube can be mind boggling and sometimes those people have prams or luggage. Getting on and off quickly is key because the doors are only open for a short time and not everyone obeys the disability access points on the platform.
From my time in London as a carer for a wheelchair aided mobility impaired person, take the black cabs and use the app to specify disability assist. It will make your trip a little more pricey but the conversation and convenience makes up for it. While only getting to use the tube once or twice was disappointing from an experience and financial point of view; the black cabs more than made up for it.