Thank you, Oron, Fleur and Trevor, for your replies.
Here is another photo showing more of the plant. It is characterised by very floppy stems, unlike a Rosa banksiae 'Alba plena' (double white) growing next to it which has quite stiff stems. Filippi says that R. banksiae var. normalis has stout thorns, whereas ours is thornless.
As to its perfume, Trevor, it seemed sort of "rosy" to me. As Fleur suggests, we will have to wait until next year to ascertain whether there is a hint of violet in the scent.
Trevor, are you by any chance a wine taster?