Same here. My usual strategy on that route is to arrive early enough to enjoy a lunch and a glass of wine in the SYD QF Flounge, one of my favourite lounges worldwide. IME it beats whatever you get aboard, even in F. Then I don't eat too much on SYD-SIN, which helps me to stay awake (and the benefit of being in F is that you can choose when you eat on that sector). I stay awake for the first 3-4 hours of SIN-LHR and sleep as close to European time as possible. Generally works well for me, I am usually pretty functional on arrival to London.

As you will be connecting at LHR, you can sleep longer on the flight and have breakfast in the CCR if that works better for you. I get off at LHR, but on many occasions with overnight flights have opted for breakfast in the arrivals lounge rather than onboard.

Am going to have to rethink my strategy though, next trip Down Under is on QR. Have always come back via Asia up to now, timings are different via the Gulf...