Cheapist time of year to fly from london to perth?

With tickets bought months in advance or by joining different air miles schemes (with air miles converted from your purchases - I traveled using this method to NY, LA and Dubai and had to pay only for charges), or I heard some air lines give the option of traveling very cheap as a courier which means you will be sitting like the cabin crew (not really a deal if you like sleeping or sitting for many hours).

The cheapest time is the time of least demand. This means basically during our winter, which is on right now - June/July/August And even then its not particularly cheap. Keep your eye on the offers made by the airlines and grab a good one if it comes up.

You are well ahead, as flying from Perth to London is always more expensive than flying from the UK! Avoid school holidays, Christmas and early late summer in Perth. The rest of the time will be as cheap as you can get.