Understandably, someone paved it and forgot about it. In fact, when I investigated, I found there were two layers of slabs in some areas and single slabs in others, with all of them simply laid on the mixture of bare earth, concrete and pipe covers that lie around the edge of the building. It's out of sight from the main garden, but is the view from one of the bedrooms, so could not really be left, or become a "glory hole", where rubbish collects and things go to die.
It's a challenge. I started by pulling out self-seeded Carex pendula which was growing up through cracks between paving slabs, and lifting slabs to reveal earth where possible. The photo shows the result and the first plant I am going to try in there: the climbing rose "Claire Austin", which should grow in shade and should also have a lovely scent.
Since the photo, I have heavily enriched the soil with compost and "soil conditioner" (which is rich, black material made from composted garden waste colected by the council) and I have planted the rose, with a framework of wires for it to climb. Once the rose gets up the wall, it will get more light.
I'm thinking about another climber for the fence area, but it will have to be a shade specialist, and most of those are pretty invasive, in my experience. Then it will be a matter of puttng things in containers on top of the slabs. Ferns and other shade-lovers, obviously, and with luck and time we will have a little green oasis in that otherwise desolate spot.