I think this may be Pink Onion Lily (Allium oleraceum) which is naturalised in the Sydney region but this I think would be the first record in our area. Would be worth pressing a sample and leaving with David Albrecht at the CSIRO Herbarium.
Actually, I have just come across Tulbaghia violacea which seems to be a very good match in terms of the peculiar structure of the flower. It is possible that it was actually planted by the previous owners, it is in a relatively cultivated area but we've never seen it flower before (in four years).
Could be. Doesbit smell of garlic? Here is a description, though the photos are not good. http://pza.sanbi.org/tulbaghia-violacea The Wikipedia article has a lousy description, but good photos. http://pza.sanbi.org/tulbaghia-violacea
Great. There was only ever the one flower stalk which by now had withered but I did, but there is a very vague garlic smell. I might relocate it to the vegie patch!