Hey, the only actual way you’ll be able to upgrade the SQ Flights from SYD-SIN-LHR are flights that are booked on an SQ number, you will not be able to upgrade the flights on a VA Number through Virgin or with krisflyer miles… the flights actually to be coded SQ and upgraded with Krisflyer miles only
Unfortunately krisflyer in all honesty isn’t great for upgrades because you have to book the most expensive economy fare, the fully flex one which at times is often substantionally more expensive than the saver fares. Fully flex is the only fare type they allow you to upgrade and again it must be on an SQ, not VA code. If the flights have a premium economy class you must book that premium economy fare to upgrade to business, otherwise you only upgrade to premium economy from flex economy
As for earning status credits it doesn’t matter if you fly on a SQ flight number, you can still credit you VA velocity number to these tickets and you will earn the full VA economy amount of status credits regardless if saver or fully flex fare, Singapore airlines is generous in this instance, so even the cheapest economy fares will earn the same amount of status credits as the full economy fares. They award status credits at the top end not the lower end which is a bonus. + you will earn VA points.
If you wish to get to London from Sydney and want to try and fly business from upgraded economy tickets you’ll have to purhase premium economy tix on SQ number, convert your VA points to Krisflyer miles and try the upgrade. As Flexi economy tickets can only be upgraded to premium economy and premium economy tickets up to business.
As a potentially cheaper alternative you might want to look at flying to Adelaide or Perth on VA, then fly to Singapore with SQ, Then onwards to Barcelona or somewhere nearby LHR, a SQ flight route or aircraft type that doesn’t have premium economy, I’m not sure if there’s any flights from SIN-LHR that don’t offer premium economy. This will allow you to jump straight from flexible economy to Business because it skips premium economy as it’s not available on such aircraft and also you miss having to pay such an expensive ticket.
Hope these suggestions help. If I’m wrong with any of the fact someone please intervene.
I constantly reiterate in all my discussions the best value to fly with Singapore airlines using krisflyer miles is with outright business award redemptions, not economy upgrades. So if you can come up with more Krisflyer miles you’ll have much better value.