Stallion,
I think you’ll find it quite a bit less than 50% as income tax rates are ‘stepped’, and slightly different between resident and non-resident.
http://www.ato.gov.au/individuals/content.asp?doc=/content/12333.htm
A quick look at the table, it can be seen that tax is only approx 30-35% (on average) for both resident & non-resident on earnings up to $180,000. Only the amount after 180,000 is taxable at 45%.
By my calculations, earning $180,000 per year @ GBP 744/day, after tax you would have around GBP 490 !! Slightly less if you’ve earned more than the $180,000.
Don’t forget, having a decent tax advisor / financial planner means that it would be possible to claim a lot of the tax back as a ‘loss’ (ie bank loan interest) on properly structured investments.