[Update March 2019: Serene has identified the building in the comments below.]
The building is near the centre of this 1947 photo:
It's a big building, with what looks like a semi-circular wall around the downhill edge.
Does anyone know what it was?
The current building on the site is Trafalgar Court. If you zoom in on the satellite view below, it looks to cover the same area as the old building and also has a curve to its downhill side:
[gmap markers=big red::22.277164525575092,114.19130535524346 |zoom=18 |center=22.277200276386548,114.19130850156762 |width=100% |height=350px |control=Small |type=Hybrid]