House construction on narrow land? 3-family house already exists

Otherwise, I would still suggest, since the rooms apparently meet all requirements, attaching an extension such as a conservatory on the ground floor in order to extend in depth and create access through the outer wall. I have seen something like this with Munich terraced houses (not real, but in a magazine)

I am slowly starting to remember: May beetle or ladybug settlement, terraced house from the 1950s: the basement was extended towards the terrace and then covered with a glass roof/conservatory, so that the conservatory below served as a base for the (new) basement and extended beyond the ground floor. That would be one way to integrate a staircase. However, this would be a matter for an experienced architect and not exactly an inexpensive affair.

.. in England's expensive cities this is done regularly.

Do you have a concrete example of that?