Yeah, I can give a bit of history if you like:

When the Gashouse bridge was built around the 1820s, the area known now as the Coleville Road now (then known as Fairy Hill) became an attractive area for the wealthy "middle class" (the owners of the mills, lawyers, minor gentry), because it was an isolated, private area, but still only a very short walk from the town.

The Quakers in particular bought up a lot of the farmland in the area, built luxury villas and either sold or let them out. The first of these was Merlin (which is still a detached house) in the 1820s, and then Springfield (now Springfield/Fairy Hill), Greenville (now Parkminster/Greenpark), Roseville, Ashbourne, etc. followed in the years after.

My understanding is that, in the decades after independence, a lot of that class would have left the country, so it became much more difficult to sell these larger houses. To remedy this, they were split up into semi-detached houses, with interior doorways being blocked off to separate the two sides, tall trees being planted across the garden to create a new boundary, a separate driveway being cut in for the other side (or I think in Fairy Hill's case, it's a repurposed archway), larger rooms being divided with really flimsy plaster/lathe walls to create more bedrooms, then later, small extensions were built on, etc.

Parkminster/Greenpark received this treatment, as well as Fairy Hill/Springfield across the road (which was also previously one single house). I don't know how widespread this practice would have been across the country, but I imagine it would have been a common enough problem.