decentlegroompleases's 1999 fare of £350 (including taxes?/plus taxes?) for LHR-SYD is remarkable - pity it's not around today.

Those familiar with the UK-Oz market know that the best deals are typically between mid-April and mid/end June. Most expensive are in December up to 24.12, with the European summer being in between.

I just can't find decentlegroomplease's BA fare of £469 including taxes for LHR-MEL and have to assume that it's not available in the UK.

The best I can find on that route are as follows: (note that prices quoted in the UK normally include taxes and charges, though Ryanair seem to be exempt from this)

£516 with Korean Air (to 6/15; book by 3/31)
£538 with Lauda Air (to 6/23)
£584 with Malaysian (to 6/30; book by 3/31)
£625 with Singapore (to 6/30; book by 3/31)

There are sometimes dramatic seat sales where you have to book within a couple of days to get bargains.