Re London busses: they're are only accessible if and when the driver is prepared to put the ramp out, and park close enough to the kerb for it to be of any use, and stop at the stop you ask them to, not the next one down the steep hill that's easier for them to pull in to. Many drivers see the whole procedure as something problematic, some sail pass pretending to not see you.
According to many of them their ramps are nearly always broken/the disabled space is already occupied by someone/thing other than a disabled person/they can't skew their schedule by manoeuvring into the stop correctly, or if you do manage to get on, you will have to make your own way back from whichever stop they feel is easier to leave you at.
(TBF anecdotally their are also exceptional drivers and routes)
They're ok for a take your time trip, but not a reliable option for most who are working and/or studying who have to be in on time.
They're also no use for those who live on a hill/ have a hill in between them and the stop, unless they have a helper.
Not having a go at anyone, just want the world to know when working/studying London wheelchair users say "can't afford taxis - I have to run a car, but if I can't park, I can't go," there are good reasons and expecting busses to be their solution isn't generally workable.