Just a thought, but if you have to start from Oslo, have you considered buying the RTW ticket originating from there rather than LHR? I did something similar a few years back (albeit from Stockholm) where ARN - LHR - SIN - SYD - HKG - LHR - ARN was £2000 cheaper in Club than a LHR originating ticket, even though it was the same BA/QF tickets. And this way, if the first flight is delayed you are I would imagine more likely to be looked after.

On the trip above we flew up from LHR to ARN on the last flight Boxing Day evening, had a drink at the hotel, and caught the same plane back down the following morning. On the way back we had a stopover in London for a week (to go back to work!) and then nipped up to Stockholm for the weekend.

As I said, just a thought!