This plant is still not in flower a month after I first found the flower stalk. However, having looked at other photos of Dianella longifolia, I think this is probably what it is. It is about 60-80 cm tall and the leaves are very long, fleshy and quite wide.
I suspect this is Dianella tasmanica. I need to see whether the sheath at the base of the leaf is basically flat as in Dianella longifolia or whether the sheath is fully occluded so that the two halves of the sheath touch (Dianella tasmanica). None of these photos show this.
The photo I have posted (same plant) - Unidentified on 4th Oct (Tidbinbilla) sighting 24449 shows the base of the leaves and may show what you need to see to determine which species this is. I will not be able to check it again for another month!