The technical term for those snippets of pavement that stick out are build-outs, but that's an engineering term to describe what they do, they build a bit of the pavement out. What is more important is why, and there the answer is, obviously, something to park on.
Here in Victoria Square, clifton, you can see a lovely example of this: the car R17KYC perfectly positioned atop one.
There's nothing technically hard about getting up here -as long as they don't have any bollards- you've just got to be convinced that you aren't going to suffer any legal or social punishment for doing so. And as we've seen on previous visits to Clifton, neither penalty appears common.
Note how this car has actually left the dropped kerb of this park-out clear. On those days there isn't anyone parked on the opposing build-out, this ensures this junction is still safe to cross.