This is a female! She has "...a silvery carapace and a silver, yellow, red and black banded upper abdomen with two longitudinal yellow stripes below. (Australian Museum)
This web was across the grass and maybe a little over the water on the bank of the river at Mt Hart.
Thank you for identifying this beautiful Spider Neil! I have never been able to get a shot of the top of these...and the bottom is never easy through the web :D These Spiders are "...named for the bluish-white cross-shaped pattern of silk through the centre of the web resembling the St Andrew's cross on the Scottish flag." (Oz Animals: http://www.ozanimals.com/Spider/St.-Andr... )