I photographed this bird (in poor light) on my first visit to the Trin Warren Tam-boore Wetlands, Royal Park, Melbourne last week. The "Friends of Royal Park" Bird Species List lists Brown Goshawk but I am wondering if this is a Collared Sparrowhawk. Unfortunately I have not seen it again.

I would humbly suggest a Collared Sparrowhawk.
If you look closely at the two images where you can see its talons, the middle talon is considerably longer that the others.
Next tell-tale id the eye, or more specifically, the eye brow, I forget the scientific term, but on a Brown Goshawk it is very heavily pronounced and overhangs the eye nearly to the point of being a verandah. Finally we have the tail feathers. When fanned out during flight the Sparrowhawk is squarish and the goshawk is rounded.
The other thing that can be quite noticeable is the reddish/brown coloration of the Sparrowhawk around the 'collar' region is more pronounced than the Goshawk.
Hope that this helps you out a bit,
Bruce.