Thanks Nick, I was considering Qantas for a trip to Sydney in April but for now I think I'll give them a miss.

FWIW, I wouldn't now use a cab from central London since the Elizabeth Line opened, it's far more reliable, not subject to traffic problems and runs every ten minutes. At LHR, I agree, security is a joke, I was recently told that they now only open priority lanes when they have enough staff and that they can be closed at any time so you are denied something you have paid for but of course no refund in rip off Britain. Airside, I would now always choose the Cathay F lounge - so much better than any other OW lounge or if you can, the Amex Centurion lounge is also pretty good.