I visited recently in my wheel chair.
The tower of London is ancient and as such has very uneven surfaces but does cater well for wheel chair access where possible. I would say you can access a good 60% of what is available.
Well we went to Alton Towers with my son who uses a power wheelchair. We had huge difficulty in the "wheelchair accessible" toilet - no room to move when you need a carer, and I don't think you would fit a manual wheelchair to the side of the toilet…