Thanks to secretflying, found this cheap one way fare to London.
Combined with Scoot, even if you add the extra baggage and meals, it is still under AU $500 from Perth and probably other Australian cities with only one stopover in Singapore.
You will have to make separate bookings with Scoot and Norwegian Air but seems to be plenty availabe, YMMV. I know it's a tough crowd here on OzBargain lately but hopefully it will be useful for some. Not sure about Scoot metal but Norwegian lag is on a 787 Dreamliner for the SIN-LGW direct flight.
nb: I wasn't sure if this qualified as a deal so posting it in forums. Mods can move it to deals section if necessary.
This was discussed in the scoot singapore deal thread. The return costs for norwegian are significantly higher unfortunately.