Flights that are not direct usually involve a change in Europe or the middle east. Even non-stop is 13 hours and just too long. I wouldn't even consider these indirect options.
The non-stop options are cheap though. With Singapore Airlines, the times are good too. It doesn't come anywhere near our low lost lux aim of maximum 9 hours per flight so it's not our first choice.
Non-Stop Direct flights
Flight Time & Airlines: ca. 13 hours. Singapore Airlines, British Airways, Quantas.
Rough Best Price 2007 low season: 640 pounds incl taxes etc [900 eur]
Rough Best Price 2007 peak season: 740 pounds incl taxes [1100 eur]
Singapore Airlines daytime flights depart both London and Singapore midday or before. Cheap fares too. This means a daytime flight, during normal daytime hours for your body clock. Unfortunately at 13 hours it's just a bit too long after you add that time for getting to the airport and the extra extra time needed for the interminable security and chevck in queues courtesy of BAA in the UK.
OK so there is a non-stop option. What about business class?
Discount Business Class
Turkish via Istanbul. 17.5 hours. Flights 4 & 12 hours. 1800 pounds incl taxes.
I.e. non stop economy + 1060 pounds peak season, + 1160 pounds off season
Or Quatar Airlines via Doha is the cheapest. But the second leg involves two flights - first Doha-Jakarta and then on to Singapore making an uncomfortable 10 hours plus for that part alone. It is cheaper at 1500 pounds inc taxes.
For this route, a stopover seems to be the best option. See it as BOGOF - buy one get one free. The flights won't cost you much more and you can visit and enjoy an extra destination or even two with a stopover each way.
Some of the best possibilities for stopovers require that you arrange a visa. This is an annoyance but mostly doable providing you are not travelling last minute.