DX Wombat: I had hoped that my Silver card etc would have reached me before I last left Oz but that was not to be. QF assured me that I WAS entitled to all the relevant priviledges as it would show up on the computer at check-in. Fine when you are leaving Oz but, as you have seen, not when trying to leave the UK via Manchester where BA is the handling agent. Part of the problem was that my ticket was issued before I gained silver status and that is likely to be repeated when I next leave the UK as I already have that ticket too.
What you were told by QF before you left was right. The BA/QF computer links are normally good enough to communicate the proper status without you having the correct card.
I've just had an experience of this working for me in October/November. I flew LHR-MIA-LHR, and qualified for QF Gold on the outbound flight. Obviously I did not have my card by the time I flew the return flight a week later. But on checking in, the boarding pass had "Sapphire" printed on it - no problems. (I also got both a through-check bag tag and boarding passes for the EK flights I was interlining to at LHR, despite the fact that they were on a completely separate booking and ticket - thank you BA for a lot of avoided hassle!)
I find that it is always worth a call to BA res to check that the QF number is properly in the BA booking computer, and that your PNR has been automatically annotated with the correct
oneworld status, as should happen as soon as the FF number goes in.