Upgrading individual segments of a RTW ticket is not permitted, except:

(a) "normal" carrier-specific upgrades (e.g., AA-elites can upgrade AA segments in accordance with normal AA upgrade rules);

(b) upgrading an economy ticket to premier economy on the BA flights (and now that it's available, on QF) from LHR to SIN/BKK to SYD etc. It's $300/leg or $450 all the way.

You're upgrading to premier economy (or 'World Traveller Plus' on BA) - you're not upgrading to business. You are correct in being suspicious that you can get a paid upgrade to business for that price.

On the other hand, if whoever told you that you can upgrade to D for $300/$450 is correct, please let us know, as we'd all like to do that!

You may want to refer to the oneworld rules (on the oneworld site) -

http://www.oneworld.com/content/libr...rule_sheet.pdf

Now that I go and check those amounts (which I'm pretty sure used to be correct), I see that they have now increased them significantly -

12. SURCHARGES
Passengers may travel in QF Premium Economy cabin, JL Premium Economy, or BA World Traveller Plus cabin for an additional charge, per flight segment of:
Sectors between SWP and Africa
Sectors between SWP and Europe
Sectors between SWP and North America
Sectors between SWP and South America
- AUD1100 GBP500 USD1000 JPY112,000


... and welcome to FT. Hopefully, you will find this place is of assistance.