Sadly, concrete tile roofs have often been substituted for slate. They are heavier than the original slate roof and require extra bracing to the roof structures. Before doing any major work on your home, if the roof has substitute concrete tiles, make sure the structure is sound. Concrete tiles collect moss - you may have noticed it scattered on the footpaths after rain - and they do not age well. When your roof needs attention, re-roof with slate.
Remember, a change in roof material will require planning permission.
The roof ridges were often finished with plain or decorated, red or blue, ridge tiles.
Slate roofs - Buckingham Street. Interesting ridge tiles - The Ark, Green Lane