After reading this I thought I'd take a look at my next couple of flights to Australia (BA 15/16). I booked on Monday in WT and WTP was £1,800 more in total than what I paid.

When I logged in before there was an offer on the return leg to upgrade to WTP for £198. I checked each leg separately - the outward was still £900 + £100 change fee and sure enough the return was £198.

I then clicked upgrade both to see what the price would be and it came out as £408. Needless to say I paid straight away and have also just selected my WTP seats in MMB.

Not complaining!!