For those who missed the 30% off ghd sale asos had earlier this month, the GHD IV Styler is already discounted to $150.41AUD - add an extra 20% off with the coupon and it comes to $120.33 which is pretty cheap for an authentic GHD.
Email says coupon expires 11am Friday 16th Dec.
Doing a quick google currency conversion, and comparing ASOS's GBP to AUD prices for their goods, it looks like you might be better off buying in GBP if you have a credit card with a good exchange rate and low or nil conversion fees (eg: 28 degrees master card).