If it actually has strong blue spark, and fuel in the cylinder, the remaining things that could prevent it from starting are wrong ignition timing (sheared flywheel key) or lack of compression (valve operation or sealing, or worn or stuck piston rings). If you do the B&S fling-it-backwards-against-compression trick you can see whether the compression is sufficient.
Too cold to start a spark ignition piston engine that is getting fuel, is pretty cold. I recall that my old 327 Camaro had problems in the Michigan winter (at minus 20 Celsius) because the fuel would not vaporise in the carburetor venturi, so it wet the spark plugs and shorted them out, but that isn't going to happen anywhere in Australia. What might be part of the problem is if you are using an old can of fuel from summer. Summer fuel has low Reid Vapour Pressure - maybe 7 p.s.i. - where in mid-winter it will probably be 14 p.s.i., and that does make a difference when cold-starting the engine. Try some current petrol - it should be at intermediate RVP by now.
