Do bear in mind you can marginally increase your Tier Point earning by switching aircraft in SIN, even if you break the journey for just 90 minutes.
This is less easy to do than used to be the case due to fewer flights/destinations and increased Minimum Connection Times (MCTs).
For instance, flying straight through SYD-LHR yields 220 TPs, whereas flying SYD-SIN changing planes and flying SIN-LHR yields 120+120=240 TPs.
You should also note that Qantas flights between LHR and Oz also qualify for the same Elite Tier bonuses for BAEC members, as BA/QF operate what is known as a JSA Joint Services Agreement on the route.
When checking fares, you may find that a oneworld explorer Round the World RTW fare, or flying via HEL on oneworld partner Finnair might be less expensive, so always bear those options in mind when speaking to your TA.
Here is the BA Tier Point and Mileage Earning calculator: